Moon

In The Legend of Zelda: Majora's Mask, the Moon is a puppet of Majora's Mask during Link's adventure in Termina. By the power of Majora's Mask, it had been pulled from its orbit, threatening to crash into Clock Town, which would obliterate the town along with most of Termina.

History
Before the events of Majora's Mask, the Skull Kid ambushed the Happy Mask Salesman and took one of his precious masks, the Majora's Mask. Even though the Skull Kid was unaware of it, Majora's Mask gradually began to take control over him, turning his harmless pranks into acts with malicious intents behind them. Eventually, the mask completely embraced the Skull Kid's mind, and using him as a puppet, Majora's Mask pulled the moon from its orbit and set its course to crash into Clock Town.

Along with his fairy companion Tatl, Link sets out to free the Four Giants in each of the temples found all over Termina. With the Giants free from their curse, the young hero and his fairy climb atop the Clock Tower on the Final Day to call upon the Giants using the Oath to Order. One by one, the Four Giants appear and stop the moon from its path of destruction.

In a turn of events, Majora's Mask realizes that the Skull Kid has become useless; thus, the Mask abandons the imp's body and transports itself inside the moon. With the moon now being possessed by the powerful Majora's Mask, it becomes too strong for the Giants to hold it back, for it threatens to continue with its plan of obliterating Termina:

"I- I shall consume... consume- consume everything."

- Moon possessed by Majora's Mask

While the Four Giants use all their might to try and sustain the evil menace, Link and Tatl decide to follow Majora into the moon. The two heroes battle against the powerful Majora and, once the malicious threat behind all of this is defeated, Link and Tatl are able to return to Termina just before the moon is overtaken by a bright light, never to be seen again.

One of the interesting points of the moon is that it always faces south. The Moon also has the same eyes as Majora's Mask, perhaps due to the curse put on it. Another interesting note is that the inside of the Moon is a beautiful meadow, hazy like a dream: the only thing to break the scene was a single tree.

Inside the Moon
Inside the moon is where the final battle takes place. It resembles a beautiful meadow, hazy like a dream. The only thing to break the scene is a single tree in the middle.

The Moon's Face
The Moon's menacing face is a small matter of debate. The main argument is to its existence; does the Moon actually have a face, or is the menacing visage a metaphor to the impending doom over Termina? Perhaps the Moon's face is an intimidating curse of Majora's Mask; an argument which has been put forward due to the similarities between the eyes on the Moon and Majora's Mask. Either way, the matching eyes are likely to be symbolic of the curse cast by Majora's Mask.

Other games

 * In The Wind Waker's Nintendo Gallery, there was a sculpture of the moon in the background behind the counter.
 * Also, the face of the Skull Kid in Twilight Princess bears a slight resemblance to the face of the Moon.

In Super Smash Bros. Melee, the stage "Termina: Great Bay" had the Moon from Majora's Mask in the background. As the match continued, it would slowly descend (not affecting the match in any way). The Four Giants would also come and push the Moon back up. There was also a trophy of the Moon that could be collected in the game. It's trophy description states that in the Moon is a plain broken by a single tree.