The following are known Action Replay Codes for Bugs Bunny In Crazy Castle 4 on Nintendo Game Boy / Color (GB / GBC). These codes were also known as GameShark Codes and in most cases will work on both devices.

Device Compatibility: Action Replay & GameShark

Infinite Keys
010806c9

Infinite Hearts
010300c9

Infinite Lives
016301c9

Infinite Corkgun
010903c9

Infinite Balloons
010904c9

Infinite Carrots
010902c9