Final Fantasy 5 Advance

Music player:
Successfully compete the game to unlock the music player option in the "Extra" menu.

Sealed Temple:
Successfully complete the game.

Necromancer job:
Defeat Enuo at the Sealed Temple.

Cloister of the Dead:
Unlock the Necromancer job.

??? Cave:
Collect all twelve legendary weapons from Kuza Castle.

Cannoneer, Gladiator, and Oracle jobs:
Enter the ??? Cave.

Bestiary:
Save the game after defeating your first enemy to unlock the "Bestiary" option at the main menu. This option shows facts about the different enemies that you have defeated.
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Hint: Stella's grave:
Go to Stella's house. Go to the left until you see a grave. Press A and you will see "Here lies Stella". [Screenshot]
Information in this section was contributed by south2.

Hint: Guaranteed Stingray encounter:
Use the following trick to encounter the "Stingray" enemy, which has the blue magic "Mighty Guard". Make your way to the world map (third world) and locate the area of the sunken tower. Save the game and shut off the Game Boy Advance. When you turn it back on, try to encounter enemies on the surface of the water around the suken tower. The first thing you run into will not be the Stingray. "Flee" or "Smoke" from this fight. The second encounter should be a Stingray.