CODES
Infinite Lives and Keys
In the options menu, press all three buttons (A, B, C) at the same time. You should hear a ringing-type confirmation noise. 
You only need to do this once; pressing the buttons again doesn't add more affects or anything. Anyway, when you start the 
game, you will have infinite lives. You can still "die", but your lives won't run any lower. Also, you will have an unlimited 
number of keys. Even if it says zero, you can use a key. It'll increase to 1 and stay there. Unless you collect more keys. 
But no matter how many keys you use, the number will never reduce to 0.