Kingdom Hearts 2: Final Mix + Cheats

How to Unlock the Fight against the ES/AU
To be able to go against this secret boss, first you must have completed the game, which means you must defeat the end boss, Xemnas. Since now you can save after defeating the game's end boss. The other objective would be to defeat the 5 Organization XIII members in their "Absent Silhouette" battles. Their battles can be accessed in different parts of the game worlds. After both of those are done, a portal will be open in Disney Castle "Hall of the CornerStone". The portal leads to the secret boss.

Organization Xll Battles - Absent Silhouette
Fight the Five Defeated Organization XIII members that were not seen in the original story.

Larxene Port Royal - Isla de la Muerte
Lexaeus Twilight Town(2nd Time) - The Sandlot
Marluxia Beast's Castle(2nd Time) - Beast's Room
Vexen Agrabah(2nd Time) - Merchant's Shop
Zexion Underworld - Cave of the Dead

Theater Mode
Theater Mode allows the viewer to view the cutscenes from the games. Kingdom Hearts II: Final Mix allows the viewer to watch them in English and Japanese. To unlock Theater Mode, one must have completed both Kingdom Hearts II: Final Mix and Kingdom Hearts Re:Chain of Memories on a memory card, to unlock Theater Mode in both games.

Theater Mode in Kingdom Hearts II: Final Mix: Complete Kingdom Hearts Re:Chain of Memories and Kingdom Hearts II: Final Mix
Theater Mode in Kingdom Hearts Re:Chain of Memories: Complete Kingdom Hearts Re:Chain of Memories and Kingdom Hearts II: Final Mix