The Goo Skulls are a species of skeleton that reside in the Vault of Bones. They are seen crawling on walls and can eject streams of adhesive "goo" originating from an organ in the rib cage from their mouths. They use this stream to both catch and encase their prey like spiders. They live in cave systems made out of this same goo.
The body of a goo skull is a typical humanoid skeleton, but the actual skulls differ between individual goo skulls. They have a pair of pale, green eyes as well as a tongue. Filling the rib cage, there is a green organ that contains their "goo." On each goo skull, there is a kitchen utensil strapped to either its head or muzzle. The Giant Goo Skull, however, has chainsaws strapped all over itself, including the head.
- Their goo appears to be highly flammable.
- They have sharp weapons (swords, axes, chainsaws, etc.) strapped to their bodies like the enemies in Adventure Time: Hey Ice King! Why'd you steal our garbage?!!
- While not being able to speak English, the Giant Goo Skull was sill able to understand and submit to Flame Princess's threats.
- In the game "Create your own game: Adventure Time" the Goo Skulls are an enemy.