I think it would fun to have a type of bonus level/challenge level in-between the the different themed floors (So after two levels). This would mainly be mix up the strategies in the game and maybe gain assets you need at the time (resources, items, characters, etc.)



Ideas;



1) Have the the crystal move slowly on a path to the exit while the characters guarded it. Maybe if they feel comfortable enough they could risk exploring other rooms to gain assets.



2) Maybe a press your luck level. You only have so much time to explore rooms freely before waves of monsters come. At any point you can head back to the starting room and leave. Maybe you can handle the first wave or so but they get harder, and the further you explore the easier is is to get caught away from the start.



3) Or a safe floor where you can talk with merchants, other surviving NPC. Maybe a character who catches rare/difficult monsters and they challenge you to fight them in an arena type battle. Or an arena where you can only use your mods and see how long you can hold out.