Majora's Mask If You Could Add a Transformation Mask...

[Dragoncat]

i may be a bad guy but a sakon mask so you can:a get into the hideout early and b: steal random items from any one you run into like he did with the bomb lady

Better But you would drop everything you stole when an enemy hit you, probably...

 

[Ouroboros]

A Minish Mask; it would shrink you just like the portals in MC to do side quests or puzzles.

 

[Kupsacker]

Doggy Mask. Invincibility against all Deku Scrubs.

 

[Twilight Gale]

Definetly Keaton Mask. I know it already excists but this one turns you into a Keaton.
Powers- Can turn invisable and only appear when you cut the grass (which enemies can't do!)

 

[ThisGuy]

Invisibility mask

 

[ZeldaFAYZ6251]

A Twili mask would be REALLY cool.

I mean can you imagine Link as a Twili, I would think it would be pretty cool...Using dark magic would be amazing!

 

[Skunk]

The Ganon Pig mask. Enough said.

 

[Terminus]

A Gerudo Mask, since the other OoT masks (except for Mask of Truth) became MM transformation masks.

A Cucco Mask.

Powers - Can float as gently as a cloud and can summon a horde of Unholy Cohorts to devour enemies with ease.

I lol'd so hard.