The GameShark is a cheating device designed for the Nintendo 64 console; it was not released for later Nintendo systems. GameShark is frequently used to hack Super Smash Bros, similar to how the Action Replay is used to hack into Melee. Apart from simply cheating at the game, it is useful for accessing content that is not normally available. Common examples include fighting in stages (such as Final Destination, the "demo" stage, or even beta versions of Kirby's level) and playing as characters (Metal Mario, Master Hand, Giant DK, or a Fighting Polygon) that cannot be accessed normally.
It was orignally designed for the Playstation and the Sega Saturn, but has been created for many other consles.
Unfortunately, the use of Gameshark with Super Smash Bros. also triggers a glitch that forces the player to play as Mario in single-player mode, even after the Gameshark has been removed. The only known way to undo this is to erase the game data.
 Uses in Project 64k and Mupen 64K
Gameshark is used often in emulators to unlock characters and stages instantly, as it is usually difficult to save with emulators in online play. To solve this, the "unlock all characters" and "Mushroom Kingdom" (to unlock item switch) cheats are switched back off and on at the beginning of the match. Failure to do this usually causes a desynch, as the first player is playing with a different set of codes than the second player and so on.