Dungeons modifiers and challenges

[Felis]

a) Difficult modifiers: At the beginning of dungeon (or during the "commence check") players can vote in options to increase the difficulty (strong enemies, permanent damage/healing debuff to all players, etc). Each modifier also increase the rewards (more XP and gil from monsters, better loot chests, etc)

You can do this already with reducing the equiped average ilevel. Except the rewards.