Final Fantasy 4 Advance Codes -

Completion bonuses:
Successfully complete the game. Continue from your cleared game file and explore the surface of the moon until you see a face-shaped rock. Enter it to access a fifty level dungeon. The "Music Player" option will also be unlocked in the "Extra" menu.

1991 Developer Team office:
After getting to the Underworld for the first time defeat Golbez in the crystal room. Get access to the armory then go down to the weapon/armor room. Move behind the pillar that is between the two shop desks. Move up from there to enter the hidden Lali Ho Pub. Next, move to the right to the dark spot on the floor. You can move through the wall from here. Climb down the stairs to reach the hidden 1991 Dev Team Office entrance. Enter the hidden area to talk to the game develppers.

Hidden magazine in Dev Team Office:
When you are in the Dev Team Office, you can find a hidden magazine in the shelf in the first room going down in the hallway to the right. If you use it, the screen will turn purple with strange music playing. Then Cecil will say "Now that is some good literature!"