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