Here is the full list of all 23 Goblins and Grottos achievements.
Picked up 15 different skulls during one play session
Blew up 20 explosive barrels during one play session.
L33t muffin collector! Found 50 muffins in the main story.
Grandmaster muffin collector! Found 100 muffins in the main story.
Killed 30 heroes.
Killed 100 heroes.
Respawned 500 times.
Discovered the Paladin's mom's credit card number.
Met the Swamp King.
Commandeered a troll.
Commandeered a sheep.
Rode in a minecart.
Met Groenk the Orc, face to face.
Discovered the muffin motherload.
Discovered the secret room of doom (and spikes).
Beat the Paladin in the final battle.
Met the gobliiins - Dwayne, Bobo and Hooter
Walked in the snow, wearing just a loincloth.
Killed Bazwaz, the stinky griefer gnome.
Discovered the joys of a lava bath.
Stabbed a hero with a knife.
Died on spikes 25 times during one play session.
Died as a chicken.