The Crystal eye is a giant crystal hidden deep within the Dungeon; its only appearance is likewise in "Dungeon." The crystal eye serves to cover a hole containing Demonic Eye Creatures. It is unknown whether the crystal eye has any real value.
It looks nothing like an eye; it resembles a huge, faceted blue gem. The crystal eye is of immense weight, consistent with its size, requiring both Finn and Jake to lift it simultaneously.
- It appears in Adventure Time: Hey Ice King! Why'd you steal our garbage?!! as a usable item. It grants temporary invincibility.