Final Fantasy III Easter Egg - How to Obtain Access to Secret Dungeon

In the Nintendo DS version of FFIII, there is a secret dungeon that contains a secret boss harder than the last boss, in order to obtain access:

1)Send a total 7 mails to another PC (one or multiple) using Mog Net.
2)Send 4 mails using Mog Net to the NPC: The 4 Elderly
3)Send 4 mails to King Arusu and after reading the fourth one, you'll unlock a quest
4)Go ride on the airship that can go underwater
5)Head for the floating island and once finding it, go exactly east..
6)You will eventually see a shadow in the waters, once you do go underwater to enter the cave
7)Soon after entering the dungeon, you will meet the secret boss

*This boss is notorious and mean. It does a total of 4 attacks per sound and also uses Meteo. Please be at a very high level before attempting this fight.