Deku Link

"Hee hee! Now that's a good look for you! You'll stay here looking like that way forever!"

— The Skull Kid

The Deku Mask is one of four of the Transformation Mask. Link becomes Deku Link in the beginning of Majora's Mask after being cursed by Skull Kid. By reclaiming your Ocarina and talking with the Happy Mask Salesman, Link turns back into regular Link and receives the Deku Mask, which has the power to transform Link back into Deku Link. Being in Deku form, Link has special abilities. By running and pressing A, Deku Link spins, which cuts grass, damages small enemies, and has the same purpose of rolling. By standing over a flower (like in the image to the right) and pressing A, Deku Link can jump inside of it and use it as a launching platform to fly. Deku Link can also jump on water for a limited time. By talking to the Great Fairy he learnes the ability of shoot out bubbles by pressing B, which can pop balloons, to talk to Tingle and other purpose.

Speculations

In the beginning of the game, only a few minutes after you get turned into a Deku Scrub, you encounter a Deku Scrub-looking tree. Tatl will mention that you share the same sad look with the tree. While wearing the Deku Mask, if you speak to the Deku Butler that shows you the way to the Mask of Scents, he mentions that you remind him of his son, who disappeared a while ago. Later on in the game, when you play the Elegy of Emptiness a statue of your current form will appear. If you play it as Goron or Zora, the statues that appears will be of Darmani or Mikau. If you are Deku Link however, a simple Deku Scrub will appear. Finally, in the end of the end credits of the game, you can see the Deku Butler kneeling beside the Deku Scrub-looking tree.

Although it's never actually mentioned in the game, only hinted at, Skull Kid probably met the Deku Butlers son on his way out to Hyrule and turned him into a tree. Then he used the spirit of the Deku Scrub to turn Link into one. When in the Goron or Zora form, the other members of the same race will recognize you as Darmani or Mikau. The Deku Butler only thinks you remind him of his son. This means that the little Deku Scrub statue that appears when you play the Elegy of Emptiness probably is the Deku Butlers son.