Here is the full list of all 18 Dungeon Defenders II achievements.
Defeat 1,000 special enemies.
Deal 5,000,000 damage with Lightning Strikes Auras.
Deal 5,000,000 damage with Flamethrower Towers.
Defeat 50 Witherbeasts before they finish burrowing.
Deal 5,000,000 damage with Explosive Traps.
Deal 5,000,000 damage with Cannonball Towers.
Activate 100 environmental traps.
On four heroes, reach level 25.
Defeat 100 Kobolds before they light their fuse.
Reach level 25 on a hero.
Reach level 15 on a hero.
Reach level 5 on a hero.