At first, Mastermind used to be a humanoid wizard with a pointy beard who used have an imperium that spanded 12 continents on a planet that had 7. After that he took the form of a levitating purple skull surrounded by green flames, which seriously impaired his abilities. Last, he took posession of Yang's body, by swapping brains with Yang. His mittens also seem to be sentient, but also serve as hands once required.