Just finish the game on Medium difficulty to unlock some bonus missions. This time you can select any character.
Cheat mode
Press Start to pause game play. Then, hold L + R and use one of the following cheat codes:
Code - Effect
Up(2), Down(2) - 20 shields
Left, Right, Left, Right - 35 random boosts
Left, Down, Right, Up, Left, Down, Right, Up - Invincibility
Right, Down, Right, Down - Maximum abilities
Right Down Left Up - Purchase all Heroes
Left Up Right Down - Take less damage than usual
Down, Down, Right, Right, Up, Up, Left, Left - Unlimited Energy
Down(2), Right(2), Up(2), Left(2) - Unlimited Superpower
Down, Left, Up, Right - Unlock all costumes
Down Right Down Left - Unlocks all cinematic scenes
Down, Left, Up, Right - Unlocks Everything
Completion bonuses
Successfully complete the game to unlock the "Continued Play" option (to allow a new game to be started with all previous stats and items unlocked" and an alternate main menu background (with characters from the game).
Fast health recovery
Upgrade your health recover and the strongest weapon for the character you are currently using. For example, upgrade the Flash's Whirlwind ability or Wonder Woman's Tiara throwing ability with Damage and Duration boosts. All the characters lose health quickly to most any kind of attacks. It is wise to have a fast recovery of health. Use the Speed Boosts in all the recovery slots.
Helpful cheats
During the gameplay, press Start. Then at the pause screen, hold L and press the following for the cheat:
All Heroes: right down left up
Invinciabilty: left down right up left down right up
Infinite power: down x2 right x2 up x2 left x2
All Alt. Costume: down left up right
All Cinematic: down right down left