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