Here is the full list of all 39 Oh My Gore achievements.
You took over 10 enemy barracks
You spent 5 hours in Oh My Gore!
You killed a unit with a charmed unit
You completed all maps on EASY
You completed all maps on NORMAL
You completed all maps on HARD
You spent 2 hours in Oh My Gore!
You killed 100 enemies with the dragon
You spawned Zombies in four barracks by magic
You killed 50 enemies by using the Cyclone
You managed to collect 30 trophies
You used the meteorshower 100 times
You used the icemagic 50 times
You spilled 10,000 gallons of blood
You spent 15 skillpoints
You covered 100 fields in cobwebs
You used Meteorshower and Bloodrain together
You completed the campaign
You managed to collect 20 trophies!
You completed 10 levels
You completed 15 levels
You have unlocked Nyrilhothep
You have unlocked Violetta
You have unlocked Mothrilastin
You looted 200,000 gold
You have spawned 100 skeletons by magic
You healed an Iron Maiden by explosives
You have unlocked Ariella
You killed 100 angels
You looted 100,000 gold
You destroyed 50 buildings
You managed to collect 10 trophies!
You completed 5 levels
You looted 50,000 gold
You have unlocked Cinda
You killed 100 elves
You killed 7 units using a meteor
You found the secret bumblebee-portrait
You have opened the credits