Here is the full list of all 14 Orc Attack: Flatulent Rebellion achievements worth 400 gamerscore.
Win a multiplayer mission (local or online).
Kill every enemy at your reach.
Bring back to life 1 Orc warrior killed in combat.
Complete a level without taking any damage.
Prevent Master Muck from taking any damage in one of the escort levels.
Fight and kill all enemies at your reach.
Hit 1000 enemies without being touched by them.
One of the Orcs must complete a full level without moving more than 3 consecutive steps.
Collect 300 coins in one combat level.
Pick every hat you can from different enemies.
Reach experience Level 15.
Play the game to the end.
Collect all the Black Stones.
Play the game to the end in Nightmare mode.