Skull Kid (race)

Skull Kids (スタルキッド) are a recurring race in the Legend of Zelda series. They are a race of diminutive, cursed skull-like beings that reside in forests. When non-fairy folk get lost in Lost Woods they become Stalfos, but Navi suggest that when children get lost in the woods they may become Skull Kids. While Skull Kids tend to be friendly towards children, they fear adults and will attack them on sight.

Biology
Skull Kids have bodies made of wood, glowing yellow eyes, and some have a beak instead of a mouth, though the Skull Kid found in Twilight Princess does have a mouth. They also are known for wearing red clothes with straw or feather adornments.

Ocarina of Time
In Ocarina of Time, Skull Kids can be found in the Lost Woods. They are found playing flute-like instruments. While Link is a child, he can interact with them; however, when he is an adult, they will fire Deku seeds at him through their instruments. As an adult, if Link kills one of them using the Biggoron's Sword or the Giant's Knife, he will receive a large Rupee.

There is one directly to the left of the entrance of the Lost Woods; he will give Link a Piece of Heart if he plays Saria's Song. If Link pursues the Happy Mask side quest, this Skull Kid will buy the Skull Mask, but he will only pay half-price.

Deeper into the woods, there are two Skull Kids on a tree stump. Link can play the Ocarina notes they provide for him to obtain another Piece of Heart.

Majora's Mask
The Skull Kid is the main antagonist in Majora's Mask. Prior to the game's events, he steals Majora's Mask from the Happy Mask Salesman. With the power of the mask, he pulls the Moon out of orbit in hopes of it hitting and destroying the land of Termina. It is heavily implied at the end of the game that this is the same Skull Kid Link met in Ocarina of Time.

Twilight Princess
After Princess Zelda heals Midna and disappears, Midna and Wolf Link head to the Faron Woods to lift the curse Zant placed on Link. Deep into the woods, they find a maze, which they can navigate with help from a Skull Kid. With the light of his lantern, and the sound of his trumpet, he leads the two through the maze in a game of hide-and-seek, releasing Puppets along the way. At the end of the maze, he fights a battle with Link; once Link has won, the Skull Kid allows him entrance to the Sacred Grove.

Later in the game, Link must return to this area of the Faron Woods. The Skull Kid again leads him through the maze, engages him in battle, and lets him into the Sacred Grove once Link prevails. The Skull Kid thanks Link for the fun and says good-bye; he is not seen or mentioned again.

The song the Skull Kid plays on his trumpet is, in fact, Saria's Song; however, the music in the background makes the notes sound almost melancholy compared to Ocarina of Time's upbeat melody.

In the manga
In Skull Kid and the Mask, a side story of two parts from Ocarina of Time manga, it is stated that while his family was on a picnic, a young boy who would become the Skull Kid Link befriends, ventured into the Lost Woods to catch a fairy. As he ran into the forest, his mother yelled at him to not go because he would get lost. Ignoring his mother's advice, he entered the forest and indeed became lost and couldn't get out. The forest was pitch black, causing him to become very scared. He entered the darkness of the forest and breathed in the dark air easily, causing him to gradually transform into a Skull Kid, the fate that befalls Hylian children who venture into the Lost Woods.

Theory
Skull Kids also slightly resemble Imp Poes, with their small shape, mischievously violent nature and (in Twilight Princess) small lanterns. This could possibly mean Skull Kids are pre-Imp Poes or their living counterparts. Supporting this, the Happy Mask Salesman (as well as a number of other characters) refers to the Skull Kid from Majora's Mask as an imp.