Butt Chest was the mystery reward that Finn and Flame Princess were trying the entire episode of, "Vault of Bones," to get. Once Flame Princess unlocked the chest, it opened it's eyes and winked at her.
At first, the Butt Chest appears to be a normal chest. Once opened, it is revealed that it’s a blue but with one eye on either cheek.
- It was one of the joke guesses that where discussed between Finn and Flame Princess when they were trying to conclude what was inside of the chest.
- The chest is seen as one of the many Easter eggs in the finale episode, "Come Along With Me," in BMO's Castle.