Win all gold belts with all regular fighters except one in legend mode to unlock Mask.
Win all gold belts with all regular fighters in legend mode to unlock Skyscrape.
Win the silver belt with all characters except one in championship mode to unlock Larry Landless.
Win the silver belt with all characters in championship mode to unlock Big John McCarthy.
Win five matches in a row to unlock fighters from the list below. Each streak of five unlocks a new guy.
Enter arcade mode. When the best record appears, press Right, Left, Right, Left, X + Y. Mask should be now be unlocked. Alternately, clear legend mode with all hidden characters.
Unlock all regular fighters, then win all Silver belts in championship mode with all of them.
Win 33 consecutive matches in arcade mode.
Lose 66 bouts in arcade mode.
Unlock all regular fighters, then win all Silver belt in championship mode with all but one of them.
Clear legend mode with all normal characters.
Win five consecutive matches to unlock the following fighters, in order. The next fighter in line will be unlocked with your next streak of five wins.