Good game + some helpful info!
When playing the before last world if you'll die you can write a code that can give you an infinite health: UP, UP, DOWN, DOWN, LEFT, RIGHT, LEFT, RIGHT, B, A. Very useful when fighting the final boss, MAC. You'll have enough tries to see how can you beat him. Oh well... there is a continue button too. Hmm... only useful if before last mission pisses you off.