Successfully complete arcade mode with a character 
to unlock their EX (Extra) form in the secret shop. 
The "EX" form is the exact same character with new, 
different, or slightly altered moves. To use a characters 
"EX" form (after purchasing it in the secret shop) go to 
the character selection screen. While choosing your 
characters, hold Start to switch from the "Normal" to 
the "EX" character. While still holding Start, press 
A, B, X, or Y to choose that character.