Game & Watch Gallery 4 (GBA)
On the title screen, after the "Play the game / View the gallery" options have appeared, press: Up, Up, Down, Down, Left, Left, Right, Right. The screen will go black, and your data will be erased. WARNING: The game doesn't ask to confirm the data erase; once the code is in, your saved data is gone.
Five secret games
There are five more games hidden in Game & Watch Gallery 4. The following is a list of the five games, and the amount of stars required to unlock each one.
Nine Museum games
Nine more games can be unlocked in the Museum (located in the Gallery Corner). To see a game, you'll need a certain amount of stars; to play the game, you'll need even more: