I had a spiffy idea for the dungeon, if it can have at least 3 floors: What about making it like a training grounds for trans characters? (but normal could enter too)
Monster or monsters at around level 20 or 30.
Double attack compared to regular monsters and double exp.
Monster or monsters at around level 70
Increased attack with increased exp. (Maybe not double because they will start to hurt)
Monster or monsters at around 90
Increased attack and possibly extra monster special skills and buffs. Beating them grants increased exp and better than average drops.
Something like this?