Unlock 99 Continues (Galaga): Before playing one of the games, repeatedly press C-Right. You will be able to get up to 99 Continues.
Unlock Super Shot (Galaga): Start Galaga and when the enemies fly onto the screen at the start of a level press A. Wait a tenth of a second and then press R. If you have done it correctly you will fire 2 shots instead of one with the single fighter. This is very effective when moving instead of staying still as you can spread out your shots. This can also be done with the double fighter as well.