Pokemon Ranger: Shadows Of Almia Codes -

Capture Arena:
Successfully complete the main storyline. You can now ride Wailord from Haruba Village to reach the Capture Arena.

Fight Darkri again:
After completing the game, go back to the top of Alturi tower. At the top, there is a man. Speak to him and you can fight Darkri again. However, once you have fought him you will lose all your Pokemon.