There are obviously difficulty levels in any game, and this is NO different: Each dungeon typically has a difficulty bar outside of it that determines how hard it is. The levels don't change, though: instead, they get flat bonus multipliers to their stats and more powerful units with more crazy capabilities and better gear to come at us. However, beating levels on harder difficulties nets us better rewards and MORE EXP, so it's worth it.

I think there are around...5. Simple, the easiest, actaully debuffs the enemies to 80% of their normal ability and prevents the really powerful enemies-Bada**es, Giant versions, generally tougher monsters, ectcedera, but prevents Legendary weapon spawning; Normal, which is what's expected of enemies outside of dungeons with no stat mods; Complex, which is the first step up and buffs enemies to 125%, makes the Bada**es appear more frequently, and makes sure no gear is below Green level rarity, and improves Legendary L00T spawn rate; Maddening, which makes it a highly unlikely event we encounter anything below Blue level rarity AND makes Legendary L00T much more likely to appear, but makes Bada** enemies a common sight and unique, super-tough enemies are now about as common as Bada**es on normal, and buffs enemy stats all around up to 150% normal capacity; and Impossible, which makes L00T almost guarenteed to be either Purple, Legendary or Mythic in rarity, but buffs enemies to 200% normal capacity, replaces all normal enemies with Bada**es, replaces all bada** enemies with the unique super-tough stuff, and even elongates the Dungeon length, making us go through new, deadlier sections reserved especially for it.

...I'm just checking here now, which do you like the most? Personally, I prefer Complex. Right mix of challenge and reward without us dying about 200 times.