Instructions
Enter cheat codes in the options menu to unlock your preferred alternate costume. For example, the code "111111" unlocks Iron Man's alternate costumes; "222222" unlocks Hulk's alternate costumes.
Open the character select screen in any game mode. Highlight the character with the alternate costume using the cursor.
Hold down the "Z" button on the Wii Nunchuk while selecting the character to use the character's alternate costume. You must keep the button held down while you drag the character's portrait to your character selection box and until the level begins.
Hold down the "C" button on the Wii Nunchuk to select your character's third alternate costume when applicable. Only certain characters, such as Wolverine and Silver Surfer, have a third costume.