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