Here is the full list of all 12 DeathSpank achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Kill Lord Von Prong
Kill 2500 Enemies
Drink 50 Potions
Discover all 30 Teleporting Outhouses
Destroy all 3 Queen Greems
Reach Level 20
Complete 6 Spelunker Quests
Finish 50 Side Quests
Kill Sergeant Orque
Dispense the Good, Vanquish the Evil
Resurrect at an Outhouse
Kill 100 Chickens