Unlocking All Extra Characters:

Use the following trick to unlock all extra characters at once. Make sure you have a saved game file for the game. Keep the disc lid open when powering on the Gamecube. Set the system date two or more months ahead from the date that
you saved the current game. Insert the game disc and start it. At the title screen, go to "Continue Game". When you get to the level selection screen, go to "Home". You will see every playable character unlocked. To confirm to the game that you
have unlocked the extra characters, just exit home, start any stage, and complete it. When you have finished, the game will confirm that you have unlocked the extra characters, as well as other cheat codes.