There are 24 Masks in The Legend of Zelda Majora'a Mask. Each Mask has think that it does I don't have a list of all the masks yet but this is what I have so far.

Deku Mask-A mask when put on turns you into a Deku Scrub this will let you fly.

Goron mask- This Mask will turn you into a Goron when you are a goron you can throw gaint rocks and do the cool curl up and roll thing.

Zora Mask-This Mask will I wonder turn you into a zora this will let swim really fast under water. And the instument you get is a guitar.

Bunny Hood-Lets you run really fast.

More info, coming, when I Get it. See anything I missed Or if I ever put anything on my site that is wrong email me at zelda_majorasmask@yahoo.ca