Majora

"According to legend... the troubles caused by Majora's Mask were so great... the ancient ones, fearing such catastrophe, sealed the mask in shadow forever, preventing its misuse. But now, that tribe from the legend has vanished, so no one really knows the true nature of the mask's power... But I feel it."

- Happy Mask Salesman talking about Majora "A puppet that can no longer be used is mere garbage. This puppet's role has just ended..."

- Majora

Majora's Mask is the main antagonist of The Legend of Zelda: Majora's Mask. It is an evil being that is responsible for possessing Skull Kid and trying to destroy Termina. It was obliterated by Fierce Deity Link and was sealed into its inanimate normal mask and was given by The Happy Mask Salesman for good.

History
This history of Majora is organized into the latest "official Zelda timeline", this may change completely in the future as the timeline given is merely meant as an example, and their have been official timelines before it.

Child Timeline
This is the timeline where Link was sent back to the past and was able to warn the Royal Family of Ganondorf's treachery, leading to the events of Twilight Princess' backstory.

Majora's Mask
The Mask was used by an ancient tribe in its rituals. Its intent is to destroy the town of Termina by bringing down the Moon on top of the city. For the majority of the game, the mask is worn by the Skull Kid on the Clock Tower, drawing the Moon to Termina. Although the Skull Kid was unaware, Majora's Mask gradually began to take complete control of his mind, turning his harmless pranks on people to acts with malicious intents. Before the game's events, Skull Kid used the power of the mask to prank and curse others around him, such as Kafei.

Decline Timeline
This is the timeline where Ganondorf killed Link in his final battle with him, leading to the Imprisoning War described in the backstory of A Link to the Past.

A Link Between Worlds
Majora's Mask (or its Lorule counterpart) appears as one of the items in Ravio's shop. It is also mentioned that the game is linked to Majora. However, this serves as nothing more than decoration, and possibly a hint about Majora's Mask 3D being in development.

Super Smash Bros. Melee
Majora's Mask appears in a stage (only playable in Event 47). If the player defeats three random opponents without losing both lives, they unlock Majora's Mask trophy.

Super Smash Bros. 4
Majora's Mask, along with Skull Kid, appears as an assist trophy in Super Smash Bros. for Wii U and 3DS. When Skull Kid is summoned, he works similarly like Tingle, but more sadistically. Its abilities include:
 * Flipping the stage upside-down.
 * Reversing the controls.
 * Turning all the fighters invisible.

Hyrule: Total War
Majora appears again in the Hyrule: Total War by Undying Nephalim, in this version it is in its true form and is the leader of the Church of Majora. This game states that the goddess sealed it away a long time ago. It is the final boss of the game, though only its followers are fought in the final level.

Personality
Majora's Mask is highly disturbed, insane, and childish. After speaking for itself for the first time near the end of the game, it declares that the Skull Kid is just its puppet, suggesting that it was actually the mask's essence itself that craved so much misery and destruction. Every power that it used seems to suggest or induce insanity and pandemonium, such as the turning of Kafei into a child mere days before his wedding, the transformation of Link into a Deku, and various other bizarre and psychopathic problems that it caused. The grotesque visage also seems to indicate madness. At the Moon, in a very peaceful but surreal meadow, Majora and the four Boss Remains take on the form of children, with Majora sitting alone and staring at the ground. It asks Link to play a game of "good guys against bad guys", where Link is the "bad guy". In combat, Majora also has a tendency to laugh to itself manically, lets out high-pitched and rambunctious shrieks when injured, and all of its forms have a very shambolic and unsettling appearance.

When asking to play their game of "good guys against bad guys", Majora freely offers Link the Fierce Deity's Mask so that he may become truly villainous and manipulative. It is suggestive that Majora has a condemnatory relationship with the being and wants to destroy him, or at least his incarnation. Majora's psychosis is only further evidenced by the offering of an item noticeably beyond his own power level. However, this is never fully elaborated upon in the game, so the nature of the two's relationship is speculative. This decision may also be made, because Majora was lonely, and was hoping that this present might make Link Majora's friend, so that he would be with others, since the other Lunar Children didn't let Majora play with them, or he just thought he was being extremely cooperative and helpful as an excuse for every trouble that they caused.

Powers and Abilities
The full scope of Majora's powers are unknown. But, they are magical in nature with dark themes. Examples, are when the Skull Kid used the mask, to seal the four giants Termina's (gods) into mask with each temple. He also used the mask's magic to curse Link into a deku and turned Kafei into a child. It even has the power to affect the afterlife, as it cursed one area of Termina with Poes and Undead.

The temples were also cursed and affected the land near each one. The Southern Swamp's water became poisoned. The Snowhead Mountain had a perpetual winter. The Great Bay's ocean had murky water. Ikana Canyon was cursed with Poes and undead. From different kinds of curses, to possessing a host as well the Mask that contains its power and spirit. Its power is also great enough to pull the moon, into Termina and was going to crash into Clock Town. After Link defeated Majora itself, the mask seemly lost its evil and dark magic.

Trivia

 * Majora is possibly the only villain in the franchise with unclear motives. Rather than try to take over the land or gain amazing power, it seems to only wish to spread as much chaos and misery as possible.
 * It is entirely possible that we may not have ever actually seen Majora, seeing as the bosses in the game are all merely things belonging to it. ie; Majora's Wrath.
 * According to a Legend of Zelda manga, Majora was a draconic being who existed before time. A mysterious entity (possibly linked to the Fierce Deity) tricked it into dancing itself to death. He then carved the mask out of Majora's armor.
 * Majora shares many similarities with Mal from Total Drama:
 * ​Both were evils from the pasts that were sealed long ago, only for them to be unleashed once more.
 * Both are greatly feared once their precense is known again.
 * Both have corrupted their hosts into doing heinous deeds. (Skull Kid for Majora; Mike for Mal)
 * Both have discarded their hosts once they no long need them.
 * Both commit their heinous deeds under the guise of the hosts they posses.
 * Both are erased from existence once they are finally defeated.
 * Both are possibly the only villains in their respective franchises with unclear motives. Unlike other villains before and after them who are usually motivated by greed or lust for power, they seem to only wish to spread as much chaos and misery as possible.
 * ​Coincidentally, both of their names begin with the letters "M" and "A".