I find it kinda of silly to have a grown man jealous of a kid. If I was calling the shots, I would have made Afiko the same age as Aang and both were friendly rivals. Like Azula, Afiko was even greater at airbending (perhaps better than the elder monks) and many of his peers (including Aang) thought he was the avatar. However, once the monks revealed that Aang was the avatar, Afiko grew envious of Aang. How could fate choose a fun-loving whimp (NOT REALLY CALLING AANG THAT) like Aang over a much more advance airbender like him? For you see Afiko REALLY wanted to be the avatar. I know, this sounds a little Lion King-ish, but back to story. So in his anger, Afiko sneaks over to the Fire Nation and....you know what else happens.

Heck, this would have been a great idea for season 4! While Aang was in animation for 100 years, Afiko was busying training himself to master all the other elements. Thus, Afiko could have been the main bad guy for season 4. Since both are airbenders, it would make sense for it to be Season Air. Afiko would the dark avatar! *catches her breath* Boy, I'm glad I finally got that out.

NOTE: This would have also been a great idea for season 4, Afiko's pupil was the main bad guy. As both became extremely jealous when the monks revealed Aang to be the avatar. Afiko's pupil could train for 100 years (in every element) and become the dark avatar. However, he would be against both sides:

Air: For the monks announcing Aang as the avatar.

Fire: For executing his master Afiko.

/copy paste from past post about a Avatar spin off.

There could be four season and each season could be set over the course of 25 years following the life of someone from one of the nations. Like a Fire Nation Soldier, a person living in the abandoned Earth Kingdom city, when people still lived there(Showing also what happened to it.) A airbender who knew Aang and what became of all the airbenders. Maybe the character could be Afiko, and his Judas betrayal, and the lives of Katara/Sokka's parents.