Bonus Wrestlers

Complete all three game modes to unlock an option to play as itchy & Scratchy for one level, and Kang for another and Smithers for another

Cheat Mode

Press Circle, Up(2), Down(2), Left, Right, Left, Right at the "Press Start" screen. This should unlock a "Bonus Match Up" at the main menu. This option allows you to play as any character and select any arena. This also can be unlocked by beating the new challenger, defender, and champion circuits.

Bumblebee Man

Play the New Challenger circuit mode, and finally you'll fight Bumblebee man, after you defeat him, save the game to unlock him as a playable character

Ned Flanders

Play the champion circuit mode, and finally you'll fight Ned Flanders, after you defeat him, save the game to unlock him as a playable character

Moe


Play the defender circuit mode, and finally you'll fight Moe, after you defeat him, save the game to unlock him as a playable character

Professor Frink

Play the champion circuit mode, and finally you'll fight Professor Frink, after you defeat him, save the game to unlock him as a playable character