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