Start a match with your second character - Hold the partner button during the character introduction sequence prior to the start of a match to start the match with your second character.

Code Effect - Hold the partner button Start the match with your second character.

Unlock secret characters by playing Arcade mode repeatedly and collecting enough points to spend in Shop.

Hakushon Daimaou Clear Arcade mode once, then purchase him for 1000 points
Ippatsuman Clear Arcade mode thrice, then purchase him for 2000 points
Saki Omokane Clear Arcade mode once, then purchase her for 1000 points
Viewtiful Joe Clear Arcade mode thrice, then purchase him for 2000 points