Deku Mask

"You’ve met with a terrible fate, haven’t you? So here I am at a loss… And now I’ve found you. Now don’t think me rude, but I have been following you… For I know of a way to return you to your former self. If you can get back the precious item that was stolen from you, I will return you to normal. In exchange… All I ask is that you also get back my precious mask that the imp stole from me."
Happy Mask Salesman

The Deku Mask is a mask from The Legend of Zelda: Majora’s Mask. This mask, shaped like the face of a Deku Scrub, allows Link to transform into one; a shape informally known as Deku Link. It is the very first mask obtained in the game, and the first of the game’s transformation masks. While wearing the mask, Link gains new abilities that are not available in his standard Hylian form.

Deku Link has a multitude of powers, the most basic of which is a brief mobile Spin Attack, which provides a boost in speed and has the ability to quickly defeat weaker enemies, stun many larger enemies, and cut grass. Additionally, Deku Link can shoot bubbles at the expense of some of his Magic Meter. The range of these bubbles increases the longer Link charges them before firing. They are somewhat inaccurate however, and will stun or bounce off extremely armored enemies rather than dealing damage. Deku Link can also use Deku Flowers, burrowing into them to hide and to launch himself into the air, damaging enemies in his path and allowing himself to fly within a certain radius using helicopter-like flowers.

[Zeldapedia]