Secret Characters and Modes of Play

Play as a StormTrooper
Set the "Player Change at Continue" option to NO, then beat the game with Han Solo on the Jedi setting.

Play as Darth Vader
Set the "Player Change at Continue" option to NO, then beat the game with Luke Skywalker on the Jedi setting.

Play as Jodo Kast
Play the survival mode and beat all 10 fighters to unlock Jodo Kast.

Play as Mara Jade
Press and hold L1 + L2 + R1 when you enter the team battle mode. Be sure the setting is on Jedi and the character change at continue option should be off. If done correctly the computer will automaticall select fighters for you and the words "Fight for Mara Jade" should be seen on the screen. Beat the computer then she will be at your control.

Play as Slave Leia
Set the "Player Change at Continue" option to NO, then beat the game with Princess Leia on the Jedi setting.

Level Select
Beat the game with Chewbacca

Big Head Mode
When selecting a character, hold select until the match starts.