The following are known Action Replay Codes for Wario Land 3 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

Have All Keys
010f5bca

Rapid Jump
010093c0

All Music Coin
01085cca

Max Coins
010904ca
019905ca

Mega Jump
01018cca
010074ca
010075ca
010076ca
010077ca