Ready 2 Rumble Boxing

Champ class boxers:
Enter championship mode and enter CHAMP as a gym name.
Exit championship mode and enter arcade mode to have access to all the boxers including Damien Black.

Gold class boxers:
Enter championship mode and enter GOLD as a gym name. Note:
This also unlocks Nat Daddy in arcade mode.

Silver class boxers:
Enter championship mode and enter SILVER as a gym name.
This also unlocks Bruce Blade in arcade mode.

Bronze class boxers:
Enter championship mode and enter BRONZE as a gym name.
This also unlocks Kemo Claw in arcade mode.