Difficulty

The game has 4 difficulty settings:

Easier

The player does 30% more damage, and receives 30% increase in healing. Achievements are not granted. TODO: Do pets also do +30%?

Normal

The default setting. The player counts as a "boss" in terms of HP per level etc.

Nightmare

All zone levels are increased by 50% + 3. Opponents have their talent levels increased by 50%. You earn nightmare achievements (if you play in Roguelike mode).

Insane

TODO: I haven't unlocked it :p You earn insane achievements (if you play in Roguelike mode).