A Skull Kid is what a child becomes after getting lost in the Lost Wood
The Skull Kid becomes a central character in Majora's Mask. Under the influence of the Majora's Mask that he stole from the Happy Mask Salesman, Skull Kid becomes a powerful sorcerer. Using this new-found might, he wreaks havoc on the four worlds of Termina, ultimately attempting to destroy it by bringing the Moon down upon the land. He appears to be the main antagonist through most of the game, though he himself is not evil and is merely being controlled by the powers of Majora's Mask.