On the Character Selection Screen, hold L and press C-Up, C-Right, C-Left, C-Down, B, A and B. The screen will flash if this code has been entered correctly. Now go to the Options Screen and there you have it!
New Characters
To get new characters hold L and press:B,C left,C up,C right, C down,A. Then keep L held down and press:A,C down,C right,C up,C left,B. Keep L pressed and press on the D-pad:up,right,down,left,right,left. To get the secret options hold L and press:C up,C right,C left,C down, B ,A . Now go to the options screen and enjoy!
Random Character Select
Press L + R simultaneously on the Character Selection Screen.
Stage Select In Multiplayer
When the "VS" Screen appears in 2-Player Mode, use the C-Buttons to alter the stage which will be used.