Press L to make your screen wider and R to return it to normal when playing a Game Boy or Game Boy Color game.
In-game reset
While playing a game, press A B Start Select to reset most Game Boy, Game Boy Color, and Game Boy Advance games.
Pause loading
At the introduction screen after the first sound swoosh, press Start Select. The Nintendo logo should disappear as it makes the Mario pause sound, and the system will pause. Then press any button after the second sound ping to bring back the Nintendo logo with another sound, and the game will continue to load. Note: This only works for Game Boy Advance games. This feature is intended for use when you link to another multi-player Game Boy Advance game that requires only one cart, without leaving your system with no game.
Other colors
Other color schemes may be selected at the Game Boy logo by pressing the following combinations:
Up: Bright Red Up A: Red Up B: Dark Red Down: Pastel Down A: Orange Down B: Gold Left: Bright Blue Left A: Dark Blue Left B: Grey Right: Bright Green Right A: Dark Green Right B: Invert Colors