Haha, I figured I'd try an Azazel run to finally see that boss rush room. By the time I got to mom, I had a homing and charming full brimstone + the lil brimstone familiar + that asshole floating eye and dark bum. I kind of blew through the rest of the game.
I fear to ask but to 100% the game, do you have to beat every path with every character on hard mode? And boss rush?
I actually don't know about all chars. but you do have to hard mode every path with The Lost. Which is well... you gotta be a god at the game to do.