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
Discover all 30 Teleporting Outhouses
Complete 6 Spelunker Quests
Destroy all 3 Queen Greems
Reach Level 20
Finish 50 Side Quests
Kill 2500 Enemies
Kill Sergeant Orque
Drink 50 Potions
Dispense the Good, Vanquish the Evil
Kill 100 Chickens
Resurrect at an Outhouse