Unused content refers to components of video games that were removed or altered before the game is released. Known info about unused content can come from a variety of sources: a developer can reveal information about the game's development, promotional material may use earlier builds of the game that contain later-removed elements, unused or incomplete code and files can be found within the finished game, and people associated with the game can leak or sell pre-release builds of the game, normally years after the game has been released.
Many elements removed from the final games have been found in all Super Smash Bros. games. Many of these have been seen in gameplay trailers, such as Kirby's "Melee" Hammer being used in midair at the E3 2006 trailer. His Hammer in midair was later changed from multiple circular swings to two powerful horizontal swings. Some of the best known beta elements include the Kirby-themed stages in Super Smash Bros., removed stages such as DUMMY and AKANEIA in Melee, and leftover character data for characters such as Mewtwo, Roy, and Dixie Kong in Brawl.