The Citadel of Bone is a large airship, owned by the malevolent Skeleton King, which operates as one of his main transportation vehicles. His pit of ooze is in the ship used to create his Formless Minions, powerful creatures to serve under his wing.First appearing in the television series, Super Robot Monkey Team Hyperforce Go, the Citadel of Bone also appears in the villain tournaments, whenever the Skeleton King uses it to travel long distances, especially when he travels throughout the galaxy's borders.