Bunny Hood
The Bunny Hood is a "mask" that has appeared in both Ocarina of Time and Majora's Mask, and also has made a cameo appearance in the Super Smash Bros. series.
Ocarina of Time
In Ocarina of Time, the mask is borrowed from The Happy Mask Shop, and subsequently can be sold to the Marathon Man for maximum Rupees. It was also unlike any other mask in the game in that it had a special property: wearing the mask would prevent Stalchildren from appearing in Hyrule Field at night.
Majora's Mask
In Majora's Mask' the mask is arguably the most useful optional mask in the game. The mask is given to you by Grog in the Cucco Shack in Romani Ranch. The first, and most useful, function of the mask is that it allows the wearer to run extremely fast, allowing Link to move across Termina on foot and still preserve time on the clock. A second minor function is to let an on-screen timer be displayed during the Postman's "count to 10 seconds" game, to aid you in stopping right at 10 seconds.
Obtaining the Mask
First, you must obtain the Bremen Mask. Once you have that, go to the Cucco Shack. Grog will talk about how he wishes he could see the cucco chicks he watches over grow to be adults. Equip the Bremen Mask and begin marching around the Shack, walking to the chicks. They will begin following you. Don't stop marching, as doing so will cause all of the chicks to disband. Once you have all 10 chicks following you, they will all turn into adults. Go talk to Grog again and he'll be amazed, and thank you with the Bunny Hood.
The Wind Waker
A hood very similar to the Bunny Hood makes a small appearance in The Wind Waker, being worn by Maggie after she's saved from the Forsaken Fortress.
Super Smash Bros. series
The Bunny Hood also makes an appearance in Super Smash Bros. Melee and Super Smash Bros. Brawl. The wearer of this item can run at a fast pace, and can jump much higher than normal.