Deku Mask: Transforms you into the stubby Deku Child (pun intended ^_^). Able to Shoot Magic Bubbbles, burrow in flowers and helicopter ability. Dogs hate you. (Get it at the beginning at the game)
Goron Mask: Change into the Goron Hero: Darmani. Smash things up, Goron ground pound or the special Goron roll. Dogs are afraid of you. (Find Darmani the ghost with the Lens of Truth in Goron Village, follow him and heal him)
Zora Mask: Change into the Zoran hero and guitarist: Mikau. Breath under water, swim like a pro, shoot boomerang fins, and use a magic forcefield to kill thinks with. Dogs love you. (Mikau is in the water to the left (Where the seagulls are) when you enter Great Bay Coast. Push him to shore and heal him)
Fierce Diety Mask: Change into Oni Link: a souped-up version of Adult Link. (Recieved when you complete all the mini dungeons on the moon)
The Other Masks:
Bremen Mask: have animals follow you when you "March". Some animals even grow up faster when you do this. (Speak to the former Windmill man of OOT on any night to get this)
Great Fairy Mask: When you wear this mask, it's hair shimmers to let you know where stray fairies are. (Get the stray fairy at Lundry Pond after you get the magic meter, and bring it back to the Great Fair in North Clocktown)
Bunny Hood: Run faster and jump further when you wear this. (Goto the Cucco Barn of Romani Ranch. Put on the Bremen mask and March. Collect all the baby Cuccos.)
Mask of Scents: Put this one on to find mushrooms easily in Southern Swamp. (Follow the Butler like Deku through a tunnel that is to the left of Deku Palace)
Romani Mask: Gain access to the Milk Bar when you wear this. (Complete Romanis and Cremias Notebook entries)
Kamaro Mask: Dance the dance of Kamaro when you wear this. (At night, goto the mushroom north of Clocktown and play the song of healing to the dancing guy)
Blast Mask: Blow things up, just like a bomb! Caution: you loose a heart when you do so! (Stop the theif in Norht Clocktown on the first night at midnight)
Kafei Mask: Ask about the missing man: Kafei when you wear this. (Speak to Madame Aroma)
Captains Hat: Speak to the undead. (Defeat the sleeping skeleton in the graveyard)
Mask of Truth: Speak to the myterious stones and some animals when you wear this. (Beat the first spider dungeon in Southern Swamp)
All Night Mask: Never fall asleep when you wear this mask. (Stop the theif on the first night, then buy it at the curiosity shop on the third night for 500 rupees)
Stone Mask: Be invisible to regular enemies. (use the lense of truth near the entrance to the graveyard and speak to the soilder. Give him a red potion.)
Keaton Mask: Wear this mask to speak to a real Keaton. (Goto Kafies house on the third day after you give the pendent to Anju)
Don Gero's Mask: Speak to frogs when wearing this. (Light all the torches in the Goron Village building, break all the spinning pots, and take the meat to the shivering goron)
Garo Mask: Wear this mask to speak to the wandering souls of the Garo (Beat the Gorman brothers on the racetrack)
Postman's Hat: Open any mailbox in Clocktown. (Get after givig the letter to Madame Arouma in the Kafei Anju quest)
Circus Leaders Mask: Wear this to ward off attackers (Go into the Milk Bar, and help the Zora with his sound check by playing the instruments while wearing each of your three transformation masks (Deku, Goron, Zora) and as Link)
Couple's Mask: (Complete Anjus notebook entry)
Gibo Mask: Be able to speak to Gibos when you wear this. (Play the song of healing for the mummy in the Canyon house)
Giants Mask: Make Link big when you wear this. (Defeat the Eyegore in Stone Tower)