Final Fantasy III Cheats

Secret Dungeon:
First, send 7 mails to another player with Mog Net. Then send 4 mails to the NPC "The 4 Elderly" and 4 to "King Arusu". After reading them, you'll unlock a quest. Travel with the underwater airship and head to the floating island. Go south and submerge at the shadow in the water to find a new dungeon and boss.

Onion Swordsman job:
Send 7 Mog Net messages to another player, and send and receive 4 mails from the NPC Topapa. After getting the mini-quest in a message, go to Uoul and talk with Topapa. Head to the cave in the north, (the further one) and kill the three bombs inside. You'll get the Onion Swordsman job, which was the default job in the old Japanese version of the game.

Duplicate items:
Has to be an item that is used in battle like elixer or attack items.  Move item u want to the top slot (either one works) then get in a battle and go to your item and press UP+A and screen should flash then press B and u got 1 more item!! also u can sell high priced items for gil.