Skull Kid
The Skull Kid is a character who has appeared in a few Zelda games. His first appearance was in Ocarina of Time, and has also appeared in Majora's Mask as the main antagonist of the game. He's also in Twilight Princess where he appeared as a background character.
Appearances
Ocarina of Time
In Ocarina of Time, three Skull Kids can be found within the Lost Woods. The first can be found through the first left-hand tunnel as you enter the forest. If Young Link stands on the tree stump and pulls out his Ocarina to play Saria's Song, the Skull Kid will give Link a Piece of Heart and befriend him. After this, the Skull Kid will buy the Skull Mask from Link, but only for 10 Rupees, half of what it costs.
The two other Skull Kids will offer to play a sing-along game, the Skull Kids will play a tune and Link will have to play back the same tune from memory; every time Link is successful the Skull Kids will add an additional note to the tune, reaching eight notes total. When Link recalls all eight notes from memory the Skull Kids will reward him with a Piece of Heart.
Skull Kids do not trust adults; when Link returns to the forest seven years later, the Skull Kids react negatively and will attack him, if Link manages to defeat a Skull Kid he will be rewarded with 50 Rupees.
Majora's Mask
The Skull Kid in Majora's Mask is known to be the same Skull Kid whom Link played Saria's Song for in Ocarina of Time, this is implied at the end of the game when the Skull Kid says that Link has the same smell as the fairy child that taught him a song in the woods.
Skull Kid had become friends with the Giants that created the four lands of Termina: swamp to the south, mountains to the north, oceans to the west, and canyons to the east. When they finished, they started to leave, but the Skull Kid tried to stop them. After they left, he started causing trouble with two fairies: Tatl and his sister Tael. The Skull Kid desired power, so stole Majora's Mask from the Happy Mask Salesman. Skull Kid became possessed by Majora's Mask's becoming its puppet, he wreaked havoc among the natives of Termina and attempted to bring the Moon crashing onto the land destroying and killing every living thing. Link managed to stop his plans by calling the Giants, at which point Majora released the Skull Kid from his grasp. After defeating Majora's Mask, Link and the Skull Kid became friends.
Twilight Princess
The Skull Kid first appears in Twilight Princess when Link enters the Lost Woods. The imp leads Link through the Lost Woods via a game of hide and seek. The game Skull Kid plays is fairly simple: there is always a clue as to where he is, as the orange glow from Skull Kid's lantern can often point Link in the direction he took off in. His horn, which resembles Deku Link's pipes in Majora's Mask, will also guide Link to him. When Link gets near him, our hero will hear him playing the familiar Saria's Song, which sets the mood perfectly. During the game of hide and seek, Skull Kid will repeatedly summon for Puppets to attack Link as he chases him, while Skull Kid will never attack Link directly.
When you return later in the game Skull Kid will once again help Link navigate the Sacred Grove, although this time he shall lead Link to the entrance of the Temple of Time. This time around, his hiding place will be harder to find. Two things give away his location: the light of his lantern and the sound of his instrument playing Saria's Song. Again, the Skull Kid never physically attacks Link, though he will summon Puppets to do the job. Every time he is hit in battle, he will summon more Puppets, but he can be beaten quickly with the bow and arrows. After defeating him the second time he will tell Link that it was fun and disappear.
Gallery
Skull Kid Artwork from Majora's Mask
In-game snapshot of the Skull Kid from Twilight Princess