About The Legend of Zelda: Majora's Mask

Gaiden translates to 'side story'.
Aliens Kidnap Epona! No, really! This game will have Link leaving his home planet and traveling to the moon.
2:48 PST Thursday Sept 02, 1999 (You heard it here first)

Majora's Mask follows Ocarina of Time. The same Link and the same Skull Kid are in both games.
Young Zelda from OoT makes are cameo appearance in a memory of Link from a time following the 'young link ending' of OoT


Tags:
The main protagonist is still a child in this game. All characters go right on living their lives regardless if the Hero of Time sees them or not during the 72 hours this game covers. The Hero can ride Epona. Tingle makes his debut in this game. The Hero once again can shoot bow and arrows. Technically, the antagonist of the game is not from the plant where Hyrule or Termina are. More specifically
A character and many cows are abducted and the character returned corresponding to the appearance of many flying saucers.
Despite the 'Gaiden' moniker, this game follows Ocarina and is a part of the Zelda series.
Perhaps the game makers initially did not want to explore the 'young link ending' to OoT since most previous games took place in the 'old Link vanished ending'. They have since all but abandon the original time line and set most newer Zelda games in the 'young link ending' time line.