You can get health regen from either a perk or the hamburger weapon. The hamburger has like a 30 second reload that you have to do manually though. I managed to beat it using the guitar weapon and focusing on crit perks and running a circle around the stage. The hammer is really good on mobs but almost impossible to kill the boss with, so don't fall for it.
Is the retry button broken for anyone else? I can run the game fine with locale, but the death screen seems to have a disabled cursor (the game still runs fine and even has UI SFX, it just doesn't have a pointer)?