If you wish to heal your characters HP and MP fully without finding an Althena statue this is the trick for you. Simply save your game and reload that saved file and your characters will be fully healed. You do not have to turn off the GBA just "save" and then choose to "load".
Hint: Duplicate Items
First, equip the item you want to duplicate and save your game. Next, go into a battle and win it. Then, unequip the item and save again. Finally, while you're still on the save/load menu (do NOT go back into the game field), load the file you have just saved. You should now have a copy of the item.
Unlock Sound Test and Music Test
Beat the game once to unlock these options.
Refresh Characters
If you wish to heal your characters HP and MP fully without finding an Althena statue this is the trick for you. Simply save your game and reload that saved file and your characters will be fully healed. You do not have to turn off the GBA just "save" and then choose to "load".