The DS version has a secret dungeon that is accessed after the following is performed.

1. Send a total 7 emails to another PC (one at a time or several at once) using Mog Net.

2. Send 4 emails using Mog Net to the NPC "The 4 Elderly".

3. Send 4 emails to King Arusu. After reading the fourth email, you'll unlock a quest.

4. Go ride on the airship that can go underwater.

5. Head for the floating island and once it appears on the screen, travel cardinally south.

6. You will eventually see a shadow in the waters. Enter it to enter the submarine cave.

7. You will meet the secret boss. This boss is notorious and mean. It does a total of four attacks per round and uses Meteo.