Beta elements are components of video games that for whatever reason, are removed or altered before that game is released. Known info about beta elements can come from a variety of sources: a developer can reveal information about the game before it leaves beta, unused code and files can be found nestled within the finished game, and people associated with the game can leak or sell test builds of the game (normally years after the game has been released). Game elements that are not used in the final build can also be found in promotional media for games.
In the Super Smash Bros. series
Many elements removed from the final games have been found in all four 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, Dr. Mario, and Dixie Kong in Brawl. The character data has caused many players to speculate that these characters were intended to be playable.