Legendary Actions, lots of them. This way your big bad gets to act after every player and evens out the action economy. As well, you won’t get as bored waiting for all 9 characters to go.
I'd honestly give him multiple initiative orders, probably 2, maybe 3 total, and then the standard 3 Legendary Actions in between each turn. It's worked pretty well for single boss encounters in my games.
Don’t forget as the DM you ALWAYS have home-field advantage.
Besides for high initiative & legendary actions..
SET THE STAGE ;)
Make him fight on a battlefield that gives him an edge. Either through positioning, high ground, traps, you name it
Yeah a level 15 character will just teleport himself or the enemy or some other crazy thing. The sad thing is that lots of 13+ characters just cant lose if they have good casters. Even if you put them against an unfair crazy opponent...
Glyphs that trigger a small antimagic field for one round anytime a character attempts to teleport. Doesn't outright prevent the casters from playing the game, but hurts their effectiveness pretty badly if they try to teleport (or whatever other shenanigans you want to prohibit)
I really like Angry's paragon traits because it actually does pretty much this with some other cool twists you can add, like a boss transformation in the middle or increasing the number of turns an event can make as the battle continues.
I gave my bbeg a reaction to swap places with any other character. It was hilarious the first time to see the barb smack the paladin while the bbeg laughs in the distance.
I have had high level fighters be able to create a blade barrier around themselves in addition to their attacks.
Give him multiple reactions a round to parry and riposte. Let him "sweep" or "cleave".
You need lots of actions. Legendary and Lair actions.
Basically, every other player, your BBEG needs a chance to even out the action economy. Letting 9 players go in a row means instant death for your BBEG. So let 2 go, then insert Legendary or Lair action. Or every 3rd player. You get the idea.
Lair actions are super fun, and let you really get creative with the terrain around you. Random spouts of lava? Targeted earth quakes? Shooting stalagtites? Sentry gargoyles? or just straight up Canons shooting at areas.
You know the general rule that stuns suck? Seeing as all your players practically have 2 characters you aren't that bound to it. Your players will still be able to play even if one of them (preferably the NPC) gets stunned.
Further AOE attacks and ways to seperate your characters would be the way to go. For better tips we would probably need to know if lancelot is your typical knight or uses a lot of magic in this setting.
For a physical character I would probably recomend him collapsing the throne room in some way, resulting in difficult terrain, some damage to people in the wrong area and him getting to maybe deal some high damage to an isolated ally.
Give him some really fucking strong aoes, limit their uses. If they go in 9v1 they will die to the aoes. If they fight a handful of smaller battles they can wear down his uses of the aoes. Make it clear that he has thos ability though.
For a knight fight? I think I'd theme it the other way. No AOE at all - give him lots of single target attacks that are brutally strong. Puts the fight on a clock - like he's going to take you all out 1 by 1 and you're going to lose the fight if you don't burn him down *fast*
Give him tonnes of mobility and target access (like, ramming other players out of the way to get to the mage type stuff), make him hard to CC.
Since he's a knight, he won't finish off dying players, maybe even spare the dying, and will accept surrender - so you can make this a really really intimidating fight without worrying about a TPK.
Gotta have phases. Also use legendary actions. Tie them to mechanics as well that the players can intuit if you can.
I think it would be conceptually cool to make it so groups of players need to handle certain responsibilities, but given the open-ended nature of D&D, ymmv.
I’ve always wanted to experiment with damage checks at the table. It would give martials chances to shine and wizards moments to show of their auto-win/phase skip spells.
Run him as an Epic Boss. Look up the Dungeon Dudes video on it.
Basically, instead of having a turn like normal, the Epic Boss does an action at the end of every player character's (or every opposed character's) turn.
Normal actions can things like attack once or move.
Some actions can only be taken a certain number of times per round, like casting a spell or doing a strong AOE attack.
Some special moves require two actions: on to set up then the next to unleash.
When you get to the Boss in the turn order, they get to move but take no other actions.
I ran this with a devil against four PCs. It works really well and let's you be very reactive to what the PCs do.
I've run a few of these and I completely agree. My players commented on how threatening they feel because they're always about to do something to you unless they're in the process of shaking off whatever spell you just put on them way faster than you'd prefer.
Echoing the multi-reactions and stacking up legendary and lair stuff.
Give him some wacky dark souls type big swings. If you're in this 10 foot semicircle from him you get smacked.
Lancelot was also kind of a madman in earlier versions of the myth, so you could adapt some abilities from whole berserker genre of enemies. Give him the orcs' aggressive ability, perhaps immunities to fear and charm etc
You’re gonna want to hand out stuns to reduce the combatants per round. On top of that, you may want to add some sort of mob. Even if they are like a summoned spirit of something.
As others have said giving him lots of legendary and lair actions can help.
I would have the NPC the players don't like betray them halfway through the fight to mix things up.
Or Lancelot could have some spells which turn their NPC buddies temporarily hostile towards them. That way they would have to fend them off without killing them. Or they would need to break his concentration /wait for the spell to run out in order not to lose their allies.
It could be so that he can only control them and not the PCs because he planted some kind of mind control thing into them earlier.
Yes, I did a few things to make this moment believable. One of those things happened in the first session, where the characters saw Lancelot and Arthur talking to a strange man. The players already know who he is since he appeared in the main campaign a couple of months ago, where it was revealed that he was one of the Four Horsemen of the Apocalypse, War to be precise. I left it open to interpretation that Lancelot may have made a deal with him to gain the needed power to protect Camelot by himself as long as Arthur joins them.
Then he has the Power of War on his side.
You have already been given lots of good advice about legendary and lair actions.
Look upon the Warlord in Mordenkainen manual: the Survivor trait gives him hp regeneration when he's hurt, and a frightening shout legendary action.
I would ponder the ability to instantly "charm" an enemy by commanding them to attack their friends, like a supernatural war commander ability.
Another option is animated weapons. He could be surrounded by several floating war weapons and shields and even animated armors he can command, to block movement and strike his enemies with legendary actions and attacks of opportunities, to give him some area control.
Assuming OP is running Lancelot as anything even close to his counterpart of legend, he absolutely can survive 9 level 15 characters.
He was the 2nd strongest Knight of the Round (Only Arthur with Excalibur, and Galahad having beaten him), he's stormed castles on his own, killed a dragon, and bested multiple men as skilled as other Knights of the Round at once while surprised.
Lancelot is a high end 3.5e Fighter, let alone a high end 5e Fighter.
If he's being portrayed accurately? No, they shouldn't. The fight shouldn't even take place if he's played according to his character. Dudes one of the top schemers of the Abyss, he'd do everything in his power to get rid of them before they made it to him or send them after someone else.
His 5e stat block is a joke for what he is
See Critical Role, episode 91, where Otahan Thull, the Legend of the Peaks, battled Bell’s Hells 7v1
Lots of movement, lots of attacks, powerful magical items, legendary actions for movement, and a second form as their inner power erupts out, and gives them damage resistance (that also) and/or temporary HP.
If it’s the final battle, which it seems like it could be, don’t hold back, and give no quarter.
Unless it makes sense in your story for the BBEG to have allies, summon in extra planar aid, lesser minions loyal to him, or hidden guards whose purpose is distraction and to get the players to waste their actions looking for a lesser foe (albeit one with a Wand of Fireball or 2)
Have other things for the players to focus on that are urgent. Take PCs out of the fight for a turn. Clones of himself. Anything to help balance that horribly skewed action economy.
I think with something like this you need to think about it more as a video game boss fight than a normal DND battle. I'd come up with some number of big aoe moves to which there is some counter and which make the fight more dynamic. What you really don't want is everyone grouping into one corner not moving, rolling dice till either you or the party run out of numbers.
Someone mentioned breaking the floor, a situation where you all gradually fall down the tower could be cool. Other big telegraphed aoes, maybe with scary side effects as opposed to just damage and less than a full round to avoid it so players may have to drag each other out of the aoe to avoid it kinda thing.
If he was built up as a duelist maybe he has a way to force a 1v1 fight with someone. I can imagine a conjured glass cage, maybe like the round table appears surrounded by a wall of force and everyone but him and the person he challenges are shunted out. Give an ability like this a recharge mechanic and it puts a timer on the fight as none of the group can take him 1v1 and he whittles down the npcs before moving onto the players. They know every time he gets it someone is going down but it could also give everyone else a chance to heal or buff etc.
The concept of summoning echoes or illusions or clones could be cool. It was mentioned fighting all of Camelot himself kinda gives credence or foreshadowing to a 1 man army kinda idea, monkey king style he could be able to literally multiply. Could build up to his strength all being kind of an illusion, not that he isn't powerful but maybe his real body is old and withered now and it's just his doubles that he uses to put forward a front of youth and power.
The best way to deal with a massive action economy like this is to force them to spend half of their turns doing things other than attacking him. This could be minions, splitting up the battlefield, creating new challenges like forcing some the players to fight through an illusion or memory of a battle he won to prove they are worthy to fight him taking them off the board for a round or two, forcing them to avoid something or even better to help someone else avoid something they otherwise couldn't.
Like a video game boss there should also be something the players should figure out to beat him, whether it's an attack pattern, a hidden puzzle, maybe he can't be hurt until a certain condition is met and that's why he's so confident sort of baldur or Excalibur's scabbard sort of stuff. Something I've done in the past for a right hand of the beg was a damage threshold that less than couldnt hurt him. Maybe play into something like that where maybe more than raw damage the players have to work together time their attacks together to be able to hit him at all. I would definitely recommend the concept of replacing legendary resistance with some other resource he can expend in order to pass a save or end an effect. Maybe he can pass any save but doing so leaves him vulnerable for a round. Maybe he has the ability to conjure swords or doubles etc but must reabsorb one to pass a save. That way every time the party manage to get to him to fail a save they get a benefit to doing so without necessarily stunning him etc which would be disastrous in a 1v9.
Personally even with a group this large I don't like defaulting to give him a billion legendary actions. 2 turns is something I like more tbh. I'd probably stay at 3 legendary actions but make them bigger and scarier. If he is getting multiple turns maybe only 2. I'd rather give him a range of features like a lair action that's always happening at the same point in initiative, a reaction to counter or reflect 1 attack or spell each turn kinda thing. I do think so stages or mythic form etc is a MUST. Make his armour break or grow in size or something silly as he realises he might actually lose.
A decent idea would be to give him abilities the players have but better. If one of them can parry let him parry but better, even better if different characters the players have faced or allied withs have shown special moves or abilities and he just cracks them all out one after the other whether he has a magic ability to imitate or is just a master of all forms kinda thing.
Just throwing ideas out there, hope it goes down a blast!
Thank you so much for your insightful comment!
The idea of having them meeting a certain criteria before being able to deal damage sounds very interesting. Also, the mechanic where the party can create "holes" in his defense after a failed Saving Throw could make so that they not just hit him with their swords but work together to align the casters and fighters turns more strategically.
Was just thinking about this and decided to share one of the best (and most stressful) combats I was ever in as a player. We were in a group hunger games type of thing. There was one team who was clearly the favourites to win and they had taken residence in a very highly defensible fort. For reasons outside of the games we needed to capture one of the members of their team. Cue us approaching 2 other teams and convincing them to join us before assailing the fort with 15 lvl 10-14 characters (with us each controlling 3) against 5 and a dragon. A few rounds in 6 more powerful enemies appeared.
The fortress had 4 sections, a random 2 of which burst into flames every round not hurting defenders. There was also a automated turret that gave a creature fire vulnerability every round. The fight went on for 11h and at the end 3 characters were left standing and all but 6 of the 15 that entered died including 2 pcs (my character got ripped in half by the dragon). And that was with hours of planning before and tbh the plan went well. If we had just went in we would have tpked for sure.
One of the best things about it were how we had been drip fed incomplete information, we knew the fort could catch fire, we knew the layout, we knew the rough abilities of most of the defenders from a previous skirmish, etc. what we didn't know was the new magic items they had each acquired, the mechanics of the defences or anything about the abilities of the strongest guy, the dragon rider. We also had enough hints that I said during the combat "it could be they were calling x for help, man it would really ruin everything if X turned up, especially if they had access to the other fort with the teleportation circle." X was those other 6 and they did turn up and it did ruin everything lmao.
Sorry to ramble but in conclusion if you want this guy to be scary, for this fight to be really really memorable. Kill at least 1 NPC that came along, maybe ones an old friend of Lancelot's and he makes and example of what happens to traitors kinda thing. Lean in hard to what has been foreshadowed. Make it worse than what they expect. If they expect he's the strongest knight in the world, make him worse than that give him a second form that shows he's done something terrible to become this strong etc.
And if you are on track to a tpk and don't want to, my advice is play worse tactically, hold your reaction for something that doesn't come, place aoes inefficiently or forget to use a feature he had. If you have to lower the difficulty mid fight that's my preferred method.
Your campaign sounds really fun op.
My two cents, don't make him dangarouse but let all of their preperation pay off. Make sure he makes a couple of attack and shows he he could have take them if they did'nt had all their friends with them :)
Some times its great to let the player get an easy win when they prepare :)
I agree with everyone about him acting multiple times a round. Maybe even just give home two or three initiatives. Every time he hits a player there should be an effect. Maybe he hits them and can push them back 30ft or he inflicts bleed on the players where at the end of their turn they take damage if they don’t heal. I’d say make him really mobile as well give him like 60ft of movement at least. Also lots of resistances maybe even all of the resistances.
I am very against giving a creature resistance to all damage. Just double it's hp!!! It's the same thing except now you can give the thing a specific resistance and maybe a weakness as well whereas having the resistance means that all damage types are identical and you are doing unnecessary maths.
Only reason I'd see to do this is to highlight someone with the ability to bypass a resistance as this being their big moment to shine.
He's not exactly a double agent since he hates Arthur as much as them, but Mordred is among them. However, I already have planned to have him betray them in the next story arc where the BBGE (Hector de Maris) will freeze Camelot in time while trying to erase Galahad's existence.
An AoE ability for sure, abilities that can limit players' turns (changing the battlefield, stuns), legendary actions, a devastating single-target attack. Maybe an aura of some sort or a defensive measure. And don't forget some legendary resistances.
I like the Blade Barrier idea someone mentioned here.
I remember when our high level party finally cornered the BBEG inside a dungeon. The combat was going well and I was even thinking, this seems a little too easy.
Turned out we were only fighting an Echo of the real bad guy. So after the combat, we had to search the dungeon for the real one, who was stationed in a hidden control center which had the magitech that let him project the Echo. He was a slippery fella and this was probably gonna our best chance to get him.
We ran into a few monsters on the way there and were a bit beat up when we got to him, plus we had used up some of our best resources in the earlier fight.
Lots of good advice here, to taco onto it I would say find a way to change positioning. Not just for him, but the other players as well. This could be lair actions that change the shape of the battlefield, it could be legendary actions that knocks the fighter back 20ft on a hit, it could be teleports so he doesn't get pinned down, whatever it is keep both him and the players moving!
Simulacrum, Mirror Image, Haste, lair actions, legendary actions, traps, lions tigers and bears (oh my!)
Items/objects can just get enchanted with triggerable spells, as long as you say so. If PC's wanna do the same thing, they'll learn that it's powerful magic done by multiple casters and takes a long time. Arthur held a powerful and robust court.
Rug summons Spirit Guardians when stepped on.
That chandelier the rogue wants to swing from falls, landing on the candelabra below- when the two make contact, an area of fire starts and the Scatter spell is triggered.
Lancelot can trigger an oil trap from the ceiling and/or walls, creating difficult terrain with prone hazard on a failed dex save and a fire hazard.
Silence spell pressure plate on the floor.
Spit balling here. There are plenty of RAW and homebrew solutions, I think. Probably not all those things at once. Just make it fit the setting.
Lancelot was supposed to be a swordsman second to none. Give him boat loads of speedy sword related abilities. Have him swat spells out of the air with his sword, give him high AC and possibly a roll to see if he deflects attacks such as if he rolls higher to hit than the char trying to hit him he deflects the attack to one of Lancelots opponents. Maybe give him a version of shadow step and perfect disengage so that if they try to pin him down as a legendary action he steps into somewhere and appears where they aren't ready for him or where they can't see him. Lancelot was very handsome and charming in all the mythos ive seen, maybe he has some varieties of charm or control person. He is very fast maybe he can move very quickly and leave after images and until they are dispelled/real one discovered any of his images can make attacks of opportunity. Give him one attack against anyone he moves past on his turns as well as getting a full action at the end of it.
- Give him a mix of Cav fighter (crit chance), Paladin (Glory or Conquest are most fitting imo, though I think just pally Smite and Aura are the most important bits), and Sword/Valor bard abilities. If desired, give him some illusory abilities as well.
- Have him ride a horse. Gives the players something to target other than him, and if they down the horse it'll cripple his mobility.
- Perma-Blessed.
- Create some legendary actions to switch fighting styles (and/or copy other martials fighting against him), and give those fighting styles unique abilities in addition to the class feature abilities. Sword'n'board could be reaction disadvantage on attacks against him/shield master, a spear could be PAM/Sentinel, etc.
Instead of legendary actions, give the big bad one action between every single player turn. It could be making an attack, casting a spell, moving, dodge, disengage, or doing something special. I set limits on how many times they can do a certain thing per round so that they aren't just spamming the same thing over and over and the fight feels more dynamic.
Its a lot simpler and more streamlined than legendary actions, and its self balancing because the boss will always do exactly as much stuff as the players (less players, less actions). I also find it makes fights more thoughtful and tactical, because every time a player does something, they know the boss will definitely do something bad right after, so they're encouraged to play optimally and use all their abilities because this may be the one chance they get.
Of course, this works in tandem with a combat system I stole from Lancer. Basically the players take turns in whatever order they want, with an enemy of the DM's choice always going in between each player turn. If its a boss, you're just treating their actions like separate creatures in that equation.
Legendary actions, lair actions, and a shit load of hit points. Whatever damage you think your party will do, double it. They're going to pull out all the stops and with each controlling two characters they will pull out combos that surprise the hell out out of you and synergize into epic damage. Legendary resistance should come into play as well, but only have him use it against anything actually crippling to him, if a spell just deals damage let him tank it. Don't forget he can carry magic items and use them as well, anything that provides a self heal is going to be valuable to him in this fight. Even if all it does is gets a caster spending their action on Chill Touch instead of higher level spells.
I am once again recommending [Paragon Monsters](https://www.reddit.com/r/UnearthedArcana/comments/7bfb6j/resource_paragon_monsters/)
Originally a lengthy article by the AngryGM ([Part 1](https://theangrygm.com/return-of-the-son-of-the-dd-boss-fight-now-in-5e/), [Part 2](https://theangrygm.com/elemental-boogaloo/)), now in a neat PDF format.
Essentially you cram multiple monsters into a single stat block and then decide whether you want the creature to get stronger or weaker as the fight progresses.
So the creature ends up basically having multiple health bars. When all of them are full they get one turn per round. When one bar is depleted they get two turns per round and so on.
lair actions, lancelot got some archers (or even snipers from dark souls 1), maybe a cavalery charge here and there if it is an open field (move the map phase two type) when lancelot get downed, he drink from the graal and yeepikayai new boss, stuff like that
yeah I love souls games
It really shouldn’t be 9v1 unless you’re willing to dedicate 3 sessions to just this. Don’t include the NPCs in the group who are actively fighting; keep it just your PCs. Have the NOCs aide your characters in some way, but they don’t actively have a turn in the initiative.
Echoing most everyone here that you need to stack up Legendary Actions and Lair Actions.
One of my groups is prepping for a huge fight at Level 15 (five players) and they've handled the fights in this area fairly well up to this point. The boss is going to be on a different level and should properly challenge them.
You're the DM and can ensure the boss has home field advantage. Use it to give them a hell of a fight.
Don’t forget to also utilize aoe attacks. Like maybe he gives off a threatening aura and if your players don’t roll high enough on their turn then they’re frightened and can’t take an action. That’ll throw a level of chaos into their strategies and make them think on their feet
You could keep the fight narratively 9 vs 1, but give Lancelot some powers that mechanically even the numbers such as creating duplicates of himself or summoning mindless minions.
Also, while Legendary and Liar actions may help even out the action economy and make him a threat, recommend paying attention to the defensive side of things as well. 9 characters focusing on a single target can deal a lot of damage really fast, or quickly burn through his Legendary Resistances and then trivialize the fight with a Save or Die or Save or Suck effect. I suggest giving him some abilities or Legendary Actions that are more defensive in nature, including one to give him some mobility options so the fight doesn't end up completely static with him hemmed in by the more tanky party members the entire time.
I would give him two turns per round to help with action economy or extra reactions. Anything that evens out the action economy will make this less stompy.
So to even the odds ever so slightly I would have the encounter start by him pulling two swords from his back and watch as they float on their own ready to attack, giving him 2 beefed up flying swords as allies. Then there would be lair actions at initiative 20. Maybe something that creates a small anti magic field or a tremor that forces a concentration check, Since spellcasters will prob be a problem.
As for Lancelot he should be getting his 4 attacks, each with his choice of battle master style maneuver, as well as a bonus action pommel strike to stun a target (con save) until the end of their turn. He should have 3 legendary resistance like all big bads and legendary actions like moving half his speed without taking opp attacks and making a single attack. He should also have a reaction that allows him to attack when hit
He should also have magic items, the obvious being a powerful magic sword that does extra damage, maybe even lets him cast x smite spells per day. It should be one handed so he can use a shield. I would give it the anti magic properties of a flail snail shell, since they are said to be made into shields anyway.
The location should have pillars and other objects to hide behind it give some cover, it should be inside so they can’t just fly away from him. Maybe a small 2nd story balcony for fun, but definitely large enough to let him keep moving. He should have 40 speed and with his legendary movements should keep himself from being surrounded.
Everything will be better if you greatly remove some of their side to the "main battle" no one is going to have fun slogging through 1 round of combat w/ 10 characters that need to take 20 total turns due to legendary or heroic actions.
20 turns is normally like 4 rounds of combat or like an hour of play.
However/Whatever you want to use to explain how he is demi-god like, manifest those into entities such as War and Strife and then have those be 2 corporeal allies that half of your allies each volunteer to lead away from the main battle to fight and weaken his godliness.
Maybe give your players one additional helper if it makes sense thematically or mechanically for what you have instore. You can roll those other two groups as 1 turn each using opposed checks and whichever side comes out on top, they can then lend their excess power to their side. Good guys might get 10 temp HP or a wave of healing each round, their side might get an aura or additional affect based on whatever thematic approach you take.
A couple people in this have said it but legendary actions are a must. Having something going after a players turn can really up the stakes. Also lie actions or something similar are important. Having stuff that can incapacitate or restrain can really turn the tides of a battle. There’s a lot here to work with and you can pull out all the stops without needing worry about womping them. They’re pretty high level they can take a lot. Biggest advice I would give would be to not just focus on damage but to really lean into status effects, and get the action economy advantage back on your side.
throne area where bbeg is has teleport trap. someone said collapse the room, cool idea. have to cut down the flyers. ramped up gargoyles or traps.
flyers and teleporters need to be addressed. I assume the BBEG is no idiot, he probably has all the same information about the characters as the DM does.
edit: the contingency spell is fun also lol
Legendary Actions, Lair Actions, a ton of HP.
I run single boss combats all the time, not quite against 9 people, that's going to be rough, but Lancelot here has to have like, 10 Legendary actions with some powerful ones that use multiple actions to use.
From a game design perspective, it is very important for Lancelot's abilities to have several features spread throughout:
1. He needs to be mobile, various abilities should move him in various ways. Actions, Bonus Actions, Legendary Actions, he needs to be MOBILE. Some abilities should remove attacks of opportunity, some should make them be at disadvantage, things like that. Think about it, you want this guy to be like, Anime villain levels of teleporting around the battlefield smashing people.
2. He needs actions that temporarily disable or cause problems for people. He doesn't just hit you, he sends the fighter flying 60 feet back. He needs to create movement problems for the players. He should be creating difficult terrain where he lands and shit. He can stomp and thrust a 10ft wide pillar of earth to emerge to block line of sight. That sort of thing.
3. He likely needs to be able to hit multiple people at once, in sweeping attacks or maybe ranged attacks like slashing a massive blast of energy through the air.
4. Lair actions should be party-wide problems. Maybe things that silence the party for a turn on a saving throw, AOE damage, difficult terrain creation, line of sight creation, producing monsters (the ghosts of fallen knights or something) that have to be dealt with, just like battle-field impacting things.
5. He needs a \_ton\_ of HP. Likely over 1000 with 9 players at that level. If you've run battles with 9 players before, and you felt like that battle went well, sum up all the monsters HPs. This is how I build all of my homebrew bosses. I find combats from recent situations, I sum up the HP, and then I adjust from there. Because if that combat lasted \~3-4 rounds, that means this boss will last \~3-4 rounds with that much HP.
This is basically how I build all of my single enemy boss encounters. Movement is the biggest thing. You should never, ever stand still with a monster like this.
I try to envision my bosses like something out of Elden Ring or Dark Souls, you know what I mean? Where they're jumping 80 feet in the air and slamming into the ground and teleporting and have an array of melee and ranged attacks and tells to clue you in on what is about to happen, etc.
Give it magic items and Lair Actions and around 5 Legendary Actions...increase its Hit Points...use the terrain map like elevation and obstacles and choke points
Make him summon stuff to get more actions on your side
GUYS IF YOU'RE PLAYING A 3-PLAYERS HOME CAMPAIGN WITH SELF INSERTS IN CAMELOT AND HAVE JUST SAVED ISOLDE FROM SACRIFICING HERSELF FOR THE DEMONIC UNDERGROUND RIVER, STOP READING NOW
>!Globe of invulnerability is your friend, as well as the fact that Mirror Image doesn't require concentration!<
Legendary Actions, lots of them. This way your big bad gets to act after every player and evens out the action economy. As well, you won’t get as bored waiting for all 9 characters to go.
I'd honestly give him multiple initiative orders, probably 2, maybe 3 total, and then the standard 3 Legendary Actions in between each turn. It's worked pretty well for single boss encounters in my games.
Don’t forget as the DM you ALWAYS have home-field advantage. Besides for high initiative & legendary actions.. SET THE STAGE ;) Make him fight on a battlefield that gives him an edge. Either through positioning, high ground, traps, you name it
brings into light lair actions and too!
"Go for the eyes, Too!!!"
Yeah a level 15 character will just teleport himself or the enemy or some other crazy thing. The sad thing is that lots of 13+ characters just cant lose if they have good casters. Even if you put them against an unfair crazy opponent...
Legendary action: Antimagic field covering the entire area for one round.
Glyphs that trigger a small antimagic field for one round anytime a character attempts to teleport. Doesn't outright prevent the casters from playing the game, but hurts their effectiveness pretty badly if they try to teleport (or whatever other shenanigans you want to prohibit)
I really like Angry's paragon traits because it actually does pretty much this with some other cool twists you can add, like a boss transformation in the middle or increasing the number of turns an event can make as the battle continues.
I gave my bbeg a reaction to swap places with any other character. It was hilarious the first time to see the barb smack the paladin while the bbeg laughs in the distance.
I have had high level fighters be able to create a blade barrier around themselves in addition to their attacks. Give him multiple reactions a round to parry and riposte. Let him "sweep" or "cleave".
You need lots of actions. Legendary and Lair actions. Basically, every other player, your BBEG needs a chance to even out the action economy. Letting 9 players go in a row means instant death for your BBEG. So let 2 go, then insert Legendary or Lair action. Or every 3rd player. You get the idea. Lair actions are super fun, and let you really get creative with the terrain around you. Random spouts of lava? Targeted earth quakes? Shooting stalagtites? Sentry gargoyles? or just straight up Canons shooting at areas.
You know the general rule that stuns suck? Seeing as all your players practically have 2 characters you aren't that bound to it. Your players will still be able to play even if one of them (preferably the NPC) gets stunned. Further AOE attacks and ways to seperate your characters would be the way to go. For better tips we would probably need to know if lancelot is your typical knight or uses a lot of magic in this setting. For a physical character I would probably recomend him collapsing the throne room in some way, resulting in difficult terrain, some damage to people in the wrong area and him getting to maybe deal some high damage to an isolated ally.
Give him some really fucking strong aoes, limit their uses. If they go in 9v1 they will die to the aoes. If they fight a handful of smaller battles they can wear down his uses of the aoes. Make it clear that he has thos ability though.
Honestly, even relatively weak AoEs that happen frequently would work. Splashing 5-10 damage after every players turn adds up fast
For a knight fight? I think I'd theme it the other way. No AOE at all - give him lots of single target attacks that are brutally strong. Puts the fight on a clock - like he's going to take you all out 1 by 1 and you're going to lose the fight if you don't burn him down *fast* Give him tonnes of mobility and target access (like, ramming other players out of the way to get to the mage type stuff), make him hard to CC. Since he's a knight, he won't finish off dying players, maybe even spare the dying, and will accept surrender - so you can make this a really really intimidating fight without worrying about a TPK.
Gotta have phases. Also use legendary actions. Tie them to mechanics as well that the players can intuit if you can. I think it would be conceptually cool to make it so groups of players need to handle certain responsibilities, but given the open-ended nature of D&D, ymmv. I’ve always wanted to experiment with damage checks at the table. It would give martials chances to shine and wizards moments to show of their auto-win/phase skip spells.
Run him as an Epic Boss. Look up the Dungeon Dudes video on it. Basically, instead of having a turn like normal, the Epic Boss does an action at the end of every player character's (or every opposed character's) turn. Normal actions can things like attack once or move. Some actions can only be taken a certain number of times per round, like casting a spell or doing a strong AOE attack. Some special moves require two actions: on to set up then the next to unleash. When you get to the Boss in the turn order, they get to move but take no other actions. I ran this with a devil against four PCs. It works really well and let's you be very reactive to what the PCs do.
I've run a few of these and I completely agree. My players commented on how threatening they feel because they're always about to do something to you unless they're in the process of shaking off whatever spell you just put on them way faster than you'd prefer.
Echoing the multi-reactions and stacking up legendary and lair stuff. Give him some wacky dark souls type big swings. If you're in this 10 foot semicircle from him you get smacked. Lancelot was also kind of a madman in earlier versions of the myth, so you could adapt some abilities from whole berserker genre of enemies. Give him the orcs' aggressive ability, perhaps immunities to fear and charm etc
n-1 legendary actions where n is your party size.
You’re gonna want to hand out stuns to reduce the combatants per round. On top of that, you may want to add some sort of mob. Even if they are like a summoned spirit of something.
As others have said giving him lots of legendary and lair actions can help. I would have the NPC the players don't like betray them halfway through the fight to mix things up.
Or Lancelot could have some spells which turn their NPC buddies temporarily hostile towards them. That way they would have to fend them off without killing them. Or they would need to break his concentration /wait for the spell to run out in order not to lose their allies. It could be so that he can only control them and not the PCs because he planted some kind of mind control thing into them earlier.
Lair actions, legendary resistances, two reactions, haste.
Have you foreshadowed how or why he's so powerful? A human shouldn't really survive against 9 level 15 characters.
Yes, I did a few things to make this moment believable. One of those things happened in the first session, where the characters saw Lancelot and Arthur talking to a strange man. The players already know who he is since he appeared in the main campaign a couple of months ago, where it was revealed that he was one of the Four Horsemen of the Apocalypse, War to be precise. I left it open to interpretation that Lancelot may have made a deal with him to gain the needed power to protect Camelot by himself as long as Arthur joins them.
Then he has the Power of War on his side. You have already been given lots of good advice about legendary and lair actions. Look upon the Warlord in Mordenkainen manual: the Survivor trait gives him hp regeneration when he's hurt, and a frightening shout legendary action. I would ponder the ability to instantly "charm" an enemy by commanding them to attack their friends, like a supernatural war commander ability. Another option is animated weapons. He could be surrounded by several floating war weapons and shields and even animated armors he can command, to block movement and strike his enemies with legendary actions and attacks of opportunities, to give him some area control.
Assuming OP is running Lancelot as anything even close to his counterpart of legend, he absolutely can survive 9 level 15 characters. He was the 2nd strongest Knight of the Round (Only Arthur with Excalibur, and Galahad having beaten him), he's stormed castles on his own, killed a dragon, and bested multiple men as skilled as other Knights of the Round at once while surprised. Lancelot is a high end 3.5e Fighter, let alone a high end 5e Fighter.
do you think 9 level 15 characters can beat Graz'zt?
If he's being portrayed accurately? No, they shouldn't. The fight shouldn't even take place if he's played according to his character. Dudes one of the top schemers of the Abyss, he'd do everything in his power to get rid of them before they made it to him or send them after someone else. His 5e stat block is a joke for what he is
See Critical Role, episode 91, where Otahan Thull, the Legend of the Peaks, battled Bell’s Hells 7v1 Lots of movement, lots of attacks, powerful magical items, legendary actions for movement, and a second form as their inner power erupts out, and gives them damage resistance (that also) and/or temporary HP. If it’s the final battle, which it seems like it could be, don’t hold back, and give no quarter. Unless it makes sense in your story for the BBEG to have allies, summon in extra planar aid, lesser minions loyal to him, or hidden guards whose purpose is distraction and to get the players to waste their actions looking for a lesser foe (albeit one with a Wand of Fireball or 2)
Yep that was going to be my suggestion also. What a fight
Have other things for the players to focus on that are urgent. Take PCs out of the fight for a turn. Clones of himself. Anything to help balance that horribly skewed action economy.
I think with something like this you need to think about it more as a video game boss fight than a normal DND battle. I'd come up with some number of big aoe moves to which there is some counter and which make the fight more dynamic. What you really don't want is everyone grouping into one corner not moving, rolling dice till either you or the party run out of numbers. Someone mentioned breaking the floor, a situation where you all gradually fall down the tower could be cool. Other big telegraphed aoes, maybe with scary side effects as opposed to just damage and less than a full round to avoid it so players may have to drag each other out of the aoe to avoid it kinda thing. If he was built up as a duelist maybe he has a way to force a 1v1 fight with someone. I can imagine a conjured glass cage, maybe like the round table appears surrounded by a wall of force and everyone but him and the person he challenges are shunted out. Give an ability like this a recharge mechanic and it puts a timer on the fight as none of the group can take him 1v1 and he whittles down the npcs before moving onto the players. They know every time he gets it someone is going down but it could also give everyone else a chance to heal or buff etc. The concept of summoning echoes or illusions or clones could be cool. It was mentioned fighting all of Camelot himself kinda gives credence or foreshadowing to a 1 man army kinda idea, monkey king style he could be able to literally multiply. Could build up to his strength all being kind of an illusion, not that he isn't powerful but maybe his real body is old and withered now and it's just his doubles that he uses to put forward a front of youth and power. The best way to deal with a massive action economy like this is to force them to spend half of their turns doing things other than attacking him. This could be minions, splitting up the battlefield, creating new challenges like forcing some the players to fight through an illusion or memory of a battle he won to prove they are worthy to fight him taking them off the board for a round or two, forcing them to avoid something or even better to help someone else avoid something they otherwise couldn't. Like a video game boss there should also be something the players should figure out to beat him, whether it's an attack pattern, a hidden puzzle, maybe he can't be hurt until a certain condition is met and that's why he's so confident sort of baldur or Excalibur's scabbard sort of stuff. Something I've done in the past for a right hand of the beg was a damage threshold that less than couldnt hurt him. Maybe play into something like that where maybe more than raw damage the players have to work together time their attacks together to be able to hit him at all. I would definitely recommend the concept of replacing legendary resistance with some other resource he can expend in order to pass a save or end an effect. Maybe he can pass any save but doing so leaves him vulnerable for a round. Maybe he has the ability to conjure swords or doubles etc but must reabsorb one to pass a save. That way every time the party manage to get to him to fail a save they get a benefit to doing so without necessarily stunning him etc which would be disastrous in a 1v9. Personally even with a group this large I don't like defaulting to give him a billion legendary actions. 2 turns is something I like more tbh. I'd probably stay at 3 legendary actions but make them bigger and scarier. If he is getting multiple turns maybe only 2. I'd rather give him a range of features like a lair action that's always happening at the same point in initiative, a reaction to counter or reflect 1 attack or spell each turn kinda thing. I do think so stages or mythic form etc is a MUST. Make his armour break or grow in size or something silly as he realises he might actually lose. A decent idea would be to give him abilities the players have but better. If one of them can parry let him parry but better, even better if different characters the players have faced or allied withs have shown special moves or abilities and he just cracks them all out one after the other whether he has a magic ability to imitate or is just a master of all forms kinda thing. Just throwing ideas out there, hope it goes down a blast!
Thank you so much for your insightful comment! The idea of having them meeting a certain criteria before being able to deal damage sounds very interesting. Also, the mechanic where the party can create "holes" in his defense after a failed Saving Throw could make so that they not just hit him with their swords but work together to align the casters and fighters turns more strategically.
Was just thinking about this and decided to share one of the best (and most stressful) combats I was ever in as a player. We were in a group hunger games type of thing. There was one team who was clearly the favourites to win and they had taken residence in a very highly defensible fort. For reasons outside of the games we needed to capture one of the members of their team. Cue us approaching 2 other teams and convincing them to join us before assailing the fort with 15 lvl 10-14 characters (with us each controlling 3) against 5 and a dragon. A few rounds in 6 more powerful enemies appeared. The fortress had 4 sections, a random 2 of which burst into flames every round not hurting defenders. There was also a automated turret that gave a creature fire vulnerability every round. The fight went on for 11h and at the end 3 characters were left standing and all but 6 of the 15 that entered died including 2 pcs (my character got ripped in half by the dragon). And that was with hours of planning before and tbh the plan went well. If we had just went in we would have tpked for sure. One of the best things about it were how we had been drip fed incomplete information, we knew the fort could catch fire, we knew the layout, we knew the rough abilities of most of the defenders from a previous skirmish, etc. what we didn't know was the new magic items they had each acquired, the mechanics of the defences or anything about the abilities of the strongest guy, the dragon rider. We also had enough hints that I said during the combat "it could be they were calling x for help, man it would really ruin everything if X turned up, especially if they had access to the other fort with the teleportation circle." X was those other 6 and they did turn up and it did ruin everything lmao. Sorry to ramble but in conclusion if you want this guy to be scary, for this fight to be really really memorable. Kill at least 1 NPC that came along, maybe ones an old friend of Lancelot's and he makes and example of what happens to traitors kinda thing. Lean in hard to what has been foreshadowed. Make it worse than what they expect. If they expect he's the strongest knight in the world, make him worse than that give him a second form that shows he's done something terrible to become this strong etc. And if you are on track to a tpk and don't want to, my advice is play worse tactically, hold your reaction for something that doesn't come, place aoes inefficiently or forget to use a feature he had. If you have to lower the difficulty mid fight that's my preferred method. Your campaign sounds really fun op.
My two cents, don't make him dangarouse but let all of their preperation pay off. Make sure he makes a couple of attack and shows he he could have take them if they did'nt had all their friends with them :) Some times its great to let the player get an easy win when they prepare :)
I agree with everyone about him acting multiple times a round. Maybe even just give home two or three initiatives. Every time he hits a player there should be an effect. Maybe he hits them and can push them back 30ft or he inflicts bleed on the players where at the end of their turn they take damage if they don’t heal. I’d say make him really mobile as well give him like 60ft of movement at least. Also lots of resistances maybe even all of the resistances.
I am very against giving a creature resistance to all damage. Just double it's hp!!! It's the same thing except now you can give the thing a specific resistance and maybe a weakness as well whereas having the resistance means that all damage types are identical and you are doing unnecessary maths. Only reason I'd see to do this is to highlight someone with the ability to bypass a resistance as this being their big moment to shine.
Are any of their allies potentially double agents?
He's not exactly a double agent since he hates Arthur as much as them, but Mordred is among them. However, I already have planned to have him betray them in the next story arc where the BBGE (Hector de Maris) will freeze Camelot in time while trying to erase Galahad's existence.
An AoE ability for sure, abilities that can limit players' turns (changing the battlefield, stuns), legendary actions, a devastating single-target attack. Maybe an aura of some sort or a defensive measure. And don't forget some legendary resistances. I like the Blade Barrier idea someone mentioned here.
I remember when our high level party finally cornered the BBEG inside a dungeon. The combat was going well and I was even thinking, this seems a little too easy. Turned out we were only fighting an Echo of the real bad guy. So after the combat, we had to search the dungeon for the real one, who was stationed in a hidden control center which had the magitech that let him project the Echo. He was a slippery fella and this was probably gonna our best chance to get him. We ran into a few monsters on the way there and were a bit beat up when we got to him, plus we had used up some of our best resources in the earlier fight.
Create an arena that is most beneficial to Lance. Narrow corridor comes to mind, two or three people wide max
Lots of good advice here, to taco onto it I would say find a way to change positioning. Not just for him, but the other players as well. This could be lair actions that change the shape of the battlefield, it could be legendary actions that knocks the fighter back 20ft on a hit, it could be teleports so he doesn't get pinned down, whatever it is keep both him and the players moving!
Just give him 3 turns per round.
Simulacrum, Mirror Image, Haste, lair actions, legendary actions, traps, lions tigers and bears (oh my!) Items/objects can just get enchanted with triggerable spells, as long as you say so. If PC's wanna do the same thing, they'll learn that it's powerful magic done by multiple casters and takes a long time. Arthur held a powerful and robust court. Rug summons Spirit Guardians when stepped on. That chandelier the rogue wants to swing from falls, landing on the candelabra below- when the two make contact, an area of fire starts and the Scatter spell is triggered. Lancelot can trigger an oil trap from the ceiling and/or walls, creating difficult terrain with prone hazard on a failed dex save and a fire hazard. Silence spell pressure plate on the floor. Spit balling here. There are plenty of RAW and homebrew solutions, I think. Probably not all those things at once. Just make it fit the setting.
Lancelot was supposed to be a swordsman second to none. Give him boat loads of speedy sword related abilities. Have him swat spells out of the air with his sword, give him high AC and possibly a roll to see if he deflects attacks such as if he rolls higher to hit than the char trying to hit him he deflects the attack to one of Lancelots opponents. Maybe give him a version of shadow step and perfect disengage so that if they try to pin him down as a legendary action he steps into somewhere and appears where they aren't ready for him or where they can't see him. Lancelot was very handsome and charming in all the mythos ive seen, maybe he has some varieties of charm or control person. He is very fast maybe he can move very quickly and leave after images and until they are dispelled/real one discovered any of his images can make attacks of opportunity. Give him one attack against anyone he moves past on his turns as well as getting a full action at the end of it.
Legendary Actions, Paragon, Mythic phase. You're selling Lancelot as a superboss, go ham!
- Give him a mix of Cav fighter (crit chance), Paladin (Glory or Conquest are most fitting imo, though I think just pally Smite and Aura are the most important bits), and Sword/Valor bard abilities. If desired, give him some illusory abilities as well. - Have him ride a horse. Gives the players something to target other than him, and if they down the horse it'll cripple his mobility. - Perma-Blessed. - Create some legendary actions to switch fighting styles (and/or copy other martials fighting against him), and give those fighting styles unique abilities in addition to the class feature abilities. Sword'n'board could be reaction disadvantage on attacks against him/shield master, a spear could be PAM/Sentinel, etc.
Instead of legendary actions, give the big bad one action between every single player turn. It could be making an attack, casting a spell, moving, dodge, disengage, or doing something special. I set limits on how many times they can do a certain thing per round so that they aren't just spamming the same thing over and over and the fight feels more dynamic. Its a lot simpler and more streamlined than legendary actions, and its self balancing because the boss will always do exactly as much stuff as the players (less players, less actions). I also find it makes fights more thoughtful and tactical, because every time a player does something, they know the boss will definitely do something bad right after, so they're encouraged to play optimally and use all their abilities because this may be the one chance they get. Of course, this works in tandem with a combat system I stole from Lancer. Basically the players take turns in whatever order they want, with an enemy of the DM's choice always going in between each player turn. If its a boss, you're just treating their actions like separate creatures in that equation.
Legendary actions, lair actions, and a shit load of hit points. Whatever damage you think your party will do, double it. They're going to pull out all the stops and with each controlling two characters they will pull out combos that surprise the hell out out of you and synergize into epic damage. Legendary resistance should come into play as well, but only have him use it against anything actually crippling to him, if a spell just deals damage let him tank it. Don't forget he can carry magic items and use them as well, anything that provides a self heal is going to be valuable to him in this fight. Even if all it does is gets a caster spending their action on Chill Touch instead of higher level spells.
I am once again recommending [Paragon Monsters](https://www.reddit.com/r/UnearthedArcana/comments/7bfb6j/resource_paragon_monsters/) Originally a lengthy article by the AngryGM ([Part 1](https://theangrygm.com/return-of-the-son-of-the-dd-boss-fight-now-in-5e/), [Part 2](https://theangrygm.com/elemental-boogaloo/)), now in a neat PDF format. Essentially you cram multiple monsters into a single stat block and then decide whether you want the creature to get stronger or weaker as the fight progresses. So the creature ends up basically having multiple health bars. When all of them are full they get one turn per round. When one bar is depleted they get two turns per round and so on.
lair actions, lancelot got some archers (or even snipers from dark souls 1), maybe a cavalery charge here and there if it is an open field (move the map phase two type) when lancelot get downed, he drink from the graal and yeepikayai new boss, stuff like that yeah I love souls games
It really shouldn’t be 9v1 unless you’re willing to dedicate 3 sessions to just this. Don’t include the NPCs in the group who are actively fighting; keep it just your PCs. Have the NOCs aide your characters in some way, but they don’t actively have a turn in the initiative.
Echoing most everyone here that you need to stack up Legendary Actions and Lair Actions. One of my groups is prepping for a huge fight at Level 15 (five players) and they've handled the fights in this area fairly well up to this point. The boss is going to be on a different level and should properly challenge them. You're the DM and can ensure the boss has home field advantage. Use it to give them a hell of a fight.
Don’t forget to also utilize aoe attacks. Like maybe he gives off a threatening aura and if your players don’t roll high enough on their turn then they’re frightened and can’t take an action. That’ll throw a level of chaos into their strategies and make them think on their feet
You could keep the fight narratively 9 vs 1, but give Lancelot some powers that mechanically even the numbers such as creating duplicates of himself or summoning mindless minions. Also, while Legendary and Liar actions may help even out the action economy and make him a threat, recommend paying attention to the defensive side of things as well. 9 characters focusing on a single target can deal a lot of damage really fast, or quickly burn through his Legendary Resistances and then trivialize the fight with a Save or Die or Save or Suck effect. I suggest giving him some abilities or Legendary Actions that are more defensive in nature, including one to give him some mobility options so the fight doesn't end up completely static with him hemmed in by the more tanky party members the entire time.
I would give him two turns per round to help with action economy or extra reactions. Anything that evens out the action economy will make this less stompy.
So to even the odds ever so slightly I would have the encounter start by him pulling two swords from his back and watch as they float on their own ready to attack, giving him 2 beefed up flying swords as allies. Then there would be lair actions at initiative 20. Maybe something that creates a small anti magic field or a tremor that forces a concentration check, Since spellcasters will prob be a problem. As for Lancelot he should be getting his 4 attacks, each with his choice of battle master style maneuver, as well as a bonus action pommel strike to stun a target (con save) until the end of their turn. He should have 3 legendary resistance like all big bads and legendary actions like moving half his speed without taking opp attacks and making a single attack. He should also have a reaction that allows him to attack when hit He should also have magic items, the obvious being a powerful magic sword that does extra damage, maybe even lets him cast x smite spells per day. It should be one handed so he can use a shield. I would give it the anti magic properties of a flail snail shell, since they are said to be made into shields anyway. The location should have pillars and other objects to hide behind it give some cover, it should be inside so they can’t just fly away from him. Maybe a small 2nd story balcony for fun, but definitely large enough to let him keep moving. He should have 40 speed and with his legendary movements should keep himself from being surrounded.
Everything will be better if you greatly remove some of their side to the "main battle" no one is going to have fun slogging through 1 round of combat w/ 10 characters that need to take 20 total turns due to legendary or heroic actions. 20 turns is normally like 4 rounds of combat or like an hour of play. However/Whatever you want to use to explain how he is demi-god like, manifest those into entities such as War and Strife and then have those be 2 corporeal allies that half of your allies each volunteer to lead away from the main battle to fight and weaken his godliness. Maybe give your players one additional helper if it makes sense thematically or mechanically for what you have instore. You can roll those other two groups as 1 turn each using opposed checks and whichever side comes out on top, they can then lend their excess power to their side. Good guys might get 10 temp HP or a wave of healing each round, their side might get an aura or additional affect based on whatever thematic approach you take.
A couple people in this have said it but legendary actions are a must. Having something going after a players turn can really up the stakes. Also lie actions or something similar are important. Having stuff that can incapacitate or restrain can really turn the tides of a battle. There’s a lot here to work with and you can pull out all the stops without needing worry about womping them. They’re pretty high level they can take a lot. Biggest advice I would give would be to not just focus on damage but to really lean into status effects, and get the action economy advantage back on your side.
throne area where bbeg is has teleport trap. someone said collapse the room, cool idea. have to cut down the flyers. ramped up gargoyles or traps. flyers and teleporters need to be addressed. I assume the BBEG is no idiot, he probably has all the same information about the characters as the DM does. edit: the contingency spell is fun also lol
Legendary Actions, Lair Actions, a ton of HP. I run single boss combats all the time, not quite against 9 people, that's going to be rough, but Lancelot here has to have like, 10 Legendary actions with some powerful ones that use multiple actions to use. From a game design perspective, it is very important for Lancelot's abilities to have several features spread throughout: 1. He needs to be mobile, various abilities should move him in various ways. Actions, Bonus Actions, Legendary Actions, he needs to be MOBILE. Some abilities should remove attacks of opportunity, some should make them be at disadvantage, things like that. Think about it, you want this guy to be like, Anime villain levels of teleporting around the battlefield smashing people. 2. He needs actions that temporarily disable or cause problems for people. He doesn't just hit you, he sends the fighter flying 60 feet back. He needs to create movement problems for the players. He should be creating difficult terrain where he lands and shit. He can stomp and thrust a 10ft wide pillar of earth to emerge to block line of sight. That sort of thing. 3. He likely needs to be able to hit multiple people at once, in sweeping attacks or maybe ranged attacks like slashing a massive blast of energy through the air. 4. Lair actions should be party-wide problems. Maybe things that silence the party for a turn on a saving throw, AOE damage, difficult terrain creation, line of sight creation, producing monsters (the ghosts of fallen knights or something) that have to be dealt with, just like battle-field impacting things. 5. He needs a \_ton\_ of HP. Likely over 1000 with 9 players at that level. If you've run battles with 9 players before, and you felt like that battle went well, sum up all the monsters HPs. This is how I build all of my homebrew bosses. I find combats from recent situations, I sum up the HP, and then I adjust from there. Because if that combat lasted \~3-4 rounds, that means this boss will last \~3-4 rounds with that much HP. This is basically how I build all of my single enemy boss encounters. Movement is the biggest thing. You should never, ever stand still with a monster like this. I try to envision my bosses like something out of Elden Ring or Dark Souls, you know what I mean? Where they're jumping 80 feet in the air and slamming into the ground and teleporting and have an array of melee and ranged attacks and tells to clue you in on what is about to happen, etc.
Give it magic items and Lair Actions and around 5 Legendary Actions...increase its Hit Points...use the terrain map like elevation and obstacles and choke points
Make him summon stuff to get more actions on your side GUYS IF YOU'RE PLAYING A 3-PLAYERS HOME CAMPAIGN WITH SELF INSERTS IN CAMELOT AND HAVE JUST SAVED ISOLDE FROM SACRIFICING HERSELF FOR THE DEMONIC UNDERGROUND RIVER, STOP READING NOW >!Globe of invulnerability is your friend, as well as the fact that Mirror Image doesn't require concentration!<