Who is the Masked One?

[Locke]

The "masked one" is only referenced by Sharp.

フラットよ わが愛しき 弟よ 死して なお 王家の復活を 夢見た おろかな兄を ゆるしてくれ・・・
Oh, Flat, my beloved younger brother. Please forgive your foolish older brother who dreamed of the restoration of the dead Royal Family.
Flat, my dear brother. Forgive your foolish brother who dreamt of the revival of the Royal Family...

・・・死者を恐れぬ者よ
…Oh, one who does not fear the dead.
...Ye who do not fear the dead...

弟の歌により 私にかけられた 呪いは解けた 全ては、お前の おかげだ
Because of my younger brother’s song, the curse put on me has been removed. It is all thanks to you.
With my brother's song, you have broken the curse that was placed upon me. It is all thanks to you.

我ら 死した者は この地に よみがえっては ならぬはず それを狂わせたのは 全ては 仮面をつけた者の 策略である
Us dead ones shouldn't be revived to this world. It was thrown out of order all due to the scheme of the one who wears a mask.
We dead should not be lingering here in this land. It was all a trick of the masked one who had upset things.

お前が ほんとうに 死者を恐れぬなら この地の 神殿におもむき 我らを 苦しめる呪いの根源を 断って欲しい
If you truly do not fear the dead, I would like you to go to the temple in this land and sever the source of the curse that is tormenting us.
If you truly do not fear the dead... I wish for you to go to the temple in this land and sever the root of the evil curse that torments us.

King Ikana isn't as specific.

王国が 滅びて われらが こんな姿に なってしまったのは・・・ このような 小さい争いのつみかさねが 原因だったではないか・・・
Our kingdom was destroyed and we became like this… Accumulating petty quarrels like this was the cause, was it not…?
The kingdom being ruined and us left in this state... Isn't it petty, little battles like this that have caused it?

仲間を 信じ それに応え 失敗を許す・・・そんなキモチが われわれの 心から消えたのは
Trusting in our comrades and responding to this by forgiving failure… These feelings disappeared from our hearts.
Believing in your friends and embracing that belief by forgiving failure... These feelings have vanished from our hearts.

何者かによって あの ロックビルの扉が 開けはなたれた 時からだ
It was ever since someone opened the door to that Rock Building.
It all happened after somebody thrust open the doors of that Stone Tower.

闇に 光をもたらす者よ 私は イカーナ王国の王 イゴース・ド・イカーナ
Oh, one who has brought light to the darkness. I am Igos do Ikana, King of the Ikana Kingdom.
You who bring light into darkness, I am the King of Ikana Kingdom, Igos du Ikana.

お前の もたらした光によって われわれに かけられた 呪縛はとけた
Due to the light you have brought, the curse that was put on us has been lifted.
The spellbinding that had been cast upon us was broken by that light which you carry.

この地に 真の光を 取り戻すには 暗黒の風がふきだすロックビルの扉 を封印しなければならぬのだ
In order to bring true light back to this land, you must seal the door to the Rock Building that is spewing out a dark wind.
To return true light to this land, you must seal the doors of Stone Tower where the winds of darkness blow through.

Someone opened the door to Stone Tower, causing Ikana Kingdom to fall and the dead to linger. The masked one tricked Sharp into trying to restore the Royal Family, or Sharp may have been attributing the curse from the Tower to him. I'm not sure. It's possible that SK opened the door just before he was banished, then returned after he got the mask to cause a little more havoc with Sharp and the King.
Fierce Deity was never said to have worn a mask. "The masked one" would have to refer to SK, whether it's inconsistent or not. We also have to assume this is following the theme throught the game of Skull Kid causing trouble. I'm not experienced enough with MM to provide any definite answers though.

 

[Oni Cucco]

I dont think that sharp was tricked by the masked one, just that the masked one open the temple and the curse began

 

[collinbollin]

Well. . .

i always thought it was twinmold that cursed it, masked, (probably) ancient, the only masked thing in there, of coarse there is a theroy somewhere where it was the gods and i dont usually combine theories but it COULD be some masked god, but i an still sticking with twinmold

 

[bbevington90]

I don't see how it could possibly not be Skull Kid wearing Majora's Mask. It's the only bad character "masked one" in the game. Look, Ikana is screwed up, but that girl in the phonograph house used to be able to run around and have fun before that curse was laid upon the land, which means it was probably recently that the curse was placed. My guess is that Ikana has been somewhat of a wasteland for quite some time after the King of Ikana died and the monarchy fell apart, and then Majora made it worse by throwing the undead there as well.

 

[Locke]

I don't see how it could possibly not be Skull Kid wearing Majora's Mask. It's the only bad character "masked one" in the game. Look, Ikana is screwed up, but that girl in the phonograph house used to be able to run around and have fun before that curse was laid upon the land, which means it was probably recently that the curse was placed. My guess is that Ikana has been somewhat of a wasteland for quite some time after the King of Ikana died and the monarchy fell apart, and then Majora made it worse by throwing the undead there as well.

IIRC, the undead were already there, and the music kept them away. SK's curse stopped the river that powered the phonograph. There do seem to be two distinct events in these quotes. One happened a while ago, one a few days ago.

 

[Rytex]

Nice arguments, though the Garo Leader did have a mask and he did wear it, as it is the one Link got from the Gorman Brothers, because the guardian to Ikana Canyon says so before he makes the tree appear. Further proof of this is that the Garo who pop up always greet you with "Master!"

It seems plausible that it would happen to be him.

 

[The Shadow]

If you truly do not fear the dead, I would like you to go to the temple in this land and sever the source of the curse that is tormenting us.
If you truly do not fear the dead... I wish for you to go to the temple in this land and sever the root of the evil curse that torments us.

Look at it, the source of the curse like all the other places is from the monsters created by Majora's Mask (While posessing SK), this means Twinmold is the cause of the curse and MM was the one to open the door, because that is really the only one to make a major amount of sense and I'm sure it would have been sealed with powerful magic to then break the seal it would require stronger magic and that is where MM came into it. I'm sure it wasn't anyone else but MM posessing the SK.

 

[Alex Arbiter]

The Masked One is mentioned threw out the game and told of reaking havoc so it Majora's mask if anything it would by the skullkid possesed by Majora's Mask.