Assuming a new Gehennom generation algorithm which generates doors, some of which must be passed in order to get through the level: have a special type of “demon key” to open doors in Gehennom. Lots of them generate in Gehennom (though not as many as there are doors; possibly a certain type of monster there generates with them so you can obtain more if you get stuck), but each key is single-use and breaks when used to open a door.