Why wait until the end? This cheat will give you End Game Rewards

All End Game Rewards - Batman: Rise of Sin Tzu for Gamecube

Here’s the cheat:

• On the Title Screen that says Press Start
• Hold the L + R
• Enter the following code: 
  • Left
  • Down
  • Left
  • Right
  • Left
  • Left
  • Down
  • Right