Move in front of the bookcase inside Casper's house. Shoot the bookcase with normal, fire, fire, ice, normal, fire, and super spirit blasts (in order). The will open to a secret room containing Lucky the Chicken.
Gameshark Codes
Must Be On ECB52F5814345B9C
Inf Comet Energy 4CC88EE01456E751
Inf Shield Energy 4CC88EE81456E7A8