The Crystalline Demon is a crystal monster who made a brief appearance in the episode "The Limit." It is a blue demon-like creature with red rubies for eyes. Since it is composed of a crystalline compound, it may originate from the Crystal Dimension. The demon is among the many inhabitants of the Labyrinth. It is unknown whether Finn and Jake encountered it during their journey through the Labyrinth, though it does appear when they walk near it while Finn is singing "Sing 'Cause Yo Mama Said." It also appears on the episode's title card.
The Crystalline Demon has crystal skin and is shaped like a demon. It has a pair of short horns, red crystal eyes, and sharp, pointy teeth.