As you can see, there's two Terras. I found this out accidentaly, and it's done like this:

 

You know you have to choose 12 characters in order to fight Kefka (if you don't choose them they'll just fight in a default order), well, if you calculate the amount of character shifts, there's a maximun number of 13 (start with 4, loose 3, then it's 7, loose 3 and then it's 10, loose 3 again and your 13th party member should fight).

 

At first I thought that if I lost that amount of characters against Kefka, I would have 3 against him in the final battle, but instead, the first character fights again. Normaly, the first character should be dead, so you would just have him/her fight again, but if your first character survives all the way to the final battle, then he's copied. Obviously, this means that it only happens in this fight, but it's still quite a bug (or glitch, I'm not too sure). Take note that this is the Advance version.

 

This is actually quite fun, especially with Terra, have them both enter Trance is enjoyable.

 

I'll leave some screenshots of the rest of the battle, just to proof it's true.

 

 

 

 

 

 

 

I was wondering, hasn't anyone found out this before?

Nope, I never had that. Of course, I was playing the SNES version, so it might just be something in the GBA version.

 

Also, when I saw the title, I thought it'd be another bug that got through the mobile port due to the lack of play testing it had. This one actually looks pretty cool.

Sweet, I'm gonna try this!

By the way, the other two party members during the final battle don't have to be dead, I just killed them so the battle focused more on both Terras and thus make it easier to get nice screenshots.