Adjust screen size
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