The Jelly Cube is a green cube-shaped blob of jelly that holds the key to a nearby locked door. It also has two eyeballs, a gauntlet and some coins that float inside of it. Whenever someone goes inside the Jelly Cube, they get stuck. Finn was never able to reach the key.
- Like other monsters in the episode, this character is based on a Dungeons & Dragons monster: the gelatinous cube.
- The Jelly Cube has an old gauntlet stuck inside of it. It may be that only the glove was lost to the cube and the person got away, or they were trapped and slowly digested by the cube and the glove is all that remains.