Full list of all 12 Orcs Must Die! achievements worth 200 gamerscore. It takes around 15-20 hours to unlock all of the achievements on Xbox 360.
Completed the campaign on Nightmare mode
Killed 30,000 orcs
Earned 5 skulls on every level on War Mage difficulty
Completed Act 3
Got 50 kills with the rolling log in one level
Completed Act 2
Gibbed more than 200 enemies on one level
Got 20 chandelier kills in one level
Completed Act 1
Killed 1,000 orcs
Won a level with 1 rift point left
Got 50 kills with explosive barrels on one level