Enter the following as a Gym Name in Championship mode:

RUMBLE_POWER    Enable Bronze Class Boxers & Kemo Claw	
RUMBLE_BUMBLE   Enable Silver Class Boxers & Bruce Blade
MOSMA!          Enable Gold Class Boxers & Nat Daddy
POD_5!          Enable Champion Class Boxers & Damien Black

Freak E. Deke        - Finish arcade mode once
Use Michael Jackson  - Finish arcade mode twice
Use G.C. Thunder     - Finish arcade mode three times
Use Wild Stubby Corly- Finish arcade mode four times
Use Shaquille O Neal - Finish arcade mode five times
Use Freedom Brock    - Finish arcade mode six times
Use Rocket Samchay   - Finish arcade mode seven times
Use Robox Rese       - Finish arcade mode eight times
Use Bill Clinton     - Finish arcade mode nine times
Use Hillary Clinton  - Finish arcade mode ten times

Enable Leprechaun:
At the Character selection screen, press X + L + R to choose Leprechaun as your cornerman.

Extra Outfits:
At the Character selection screen, press X + Y to choose an alternate outfit.

Choose your ring:
In two-player arcade mode, hold the following while selecting your characters.

L       Two-tiered arena
R       Championship arena
L+R     Gym

Holiday backgrounds:
Set the internal Dreamcast clock on Christmas (Dec 25). Now start a prize fight, and you'll find Xmas trees in the background. Set the clock on Halloween (Oct 31) and you'll find skeletons in the arena.

Extra art:
Put the game disk into a PC CD-ROM Drive. Look in the directory called 'extras' to find some cool Ready 2 Rumble wallpaper.

Cheap training:
In Training, highlight the Rumble Aerobics Training and press Left and then quickly press A. If you did it fast enough, you will buy the Rumble Mass Nutrition Regime (which costs $25,000) for $500! This will boost your strength and experience very quickly.

Thanks to Revolution readers Ian Gaglione, hotboy, Martin Bradshaw, BigRockFan, M. Brandon Williams, TomW, Jesse, Nicko, Alex and ItchyLegs!