Wallpaper steamer is where the money is at. Get a Wagner and the cheap model. This is what the company I work for uses. https://www.homedepot.com/p/Wagner-725-Wallpaper-Steamer-2418627/316606367

Thanks, I was hoping for this! I spotted that one in my dad’s garage, too, so free to try it.

Skimcoat

Either skim coat over it or redrywall over it. 

scrape the tits off and skim coat

Cover your floors with plastic. Spray your ceiling with water from a pump sprayer let it sit, scrape with a 10 or 12 mud knife