Game & Watch Gallery 3 (GB)

Memory clear
To erase all the saved data on the battery, on the title screen press Up Up Down Down Left Left Right Right.
Toggle music
On the "game options" screen, press Select to toggle the music on or off. A note will be in the upper-left corner when the music is on.
Interrupt save
During a game, press Start to pause, then turn off the Game Boy. When you turn it back on, you'll be able to start that game from where you left off.