I dono if this had been discuss already.
In episodes 19-20. Koh the Face-Stealer had made his appearence.

http://youtube.com/results?search_query=avatar+120&search=Search

When Angg faced Koh to find out about the secret of the moon sprite, Koh talked about a past avatar named ??? about 750 years before Angg. That avatar tried to kill Koh for stealing his lover's face. Koh showed that face to Angg right after showing that past avatar's face. At the end when Angg is leaving, Koh said, "We shall meet again."

I found that part is highly forshadowing what going to happen in the future. Possibly in the future, Koh is going to steal Angg's lover face (I not going to say who). Koh will be a very powerful opponent because in the past 10,000 years, no one was about to defeat him.

If this had been posted before, I want sincerely apologize to those who are offended.??

I am offended.

we have no proof that the face shown before the avatar's lover's face is that previous avatar. and, sure, Aang might very well meet Koh again, but I doubt he's going to take away his lover's face.

He needs to just choose one face and stick with it. In fact, he needs to I don't know...acually find a body before a face. I mean, what kind of person would go out with a centipede, yet face is good looking?! XD

Of course, it just a theory and assume facts.
It just my opinion of forsadowing what going to happen.
I not trying to convince u to believe those fact nor to believe that exactly what going to happen.

Just what to hear your opinion.

I believe this can actually be a great story for after defeat of fire lord.
But you never know what going to happen in this unpredictable show.

It's never actually stated that Koh took the previous Avatar's face.?? He could have been killed during the fight or figured out some way to protect himself.?? As various episodes have shown, the Avatar does not retain all memories from past lives.?? Even when a previous Avatar takes over Aang's body, he doesn't recall anything that happens during that time.?? You could even ask why he took the face of what looks to be a Fire Nation person when he said they'd meet again.?? It's possible that Aang isn't the second Avatar he has met.?? It's even possible the one from 800 years ago isn't even the second.?? Koh is one of the oldest spirits in existence, if not the oldest.?? Who knows how many of them have sought Koh for his knowledge.

stealing kataras face would ruin the show..