I tried leveling my plague doctor in the respite dungeon. DON'T! When you fight the derby demon, she will get dark ghost, and never die. The counter stays at 1. Dark ghost keeps a character alive as long as it isn't hit with permadeath and she is immune to permadeath. I don't know why the counter didn't go down though. (I realize that I can use a character that disables passives bu I didn't have one with me in that battle. )