I remember that at some point of the game, the character sprites changes. I remember that the Black Mage changed into an unhooded Black mage which was awesome yet later, he changed back.

Could anyone tell me why this occurred?

Once you've talked with Bahamut and done all the stuff he requires, your characters get upgraded classes. Thieves into Ninjas, Mages into Wizards, Fighters into Knights, and Black Belts into something cool. They're just better versions of your characters.

Why they changed back? I have no idea.. sorry..

I don't remember them changing back...

I remember my black mage did. I was so upset. Maybe he didn't like to show his face or something.

I recall I was in a battle with some monsters and that's when he reverted back to his black mage state. Anyway, my NES was old and I bought that game from Funco Land. Maybe it was a glitch.

definitely should not have changed back. once they get the upgraded classes, they should stay that way. weird..

Did this occur when you turned the game on, or during the game?

During the game. It was in battle. The black mage received damage from these monsters and then reverted back. The whole ordeal is foggy because it was a long time ago.

I don't understand it myself because it was only my black mage.

Welll...Gee ...That's either some glitch...or your game does not like you.