Here is a list of a few things that could indicate why Tenzin could be Amon:
- Tenzin is never there when Amon is.
- Amon can dodge lightning, lightning is REALLY fast you would have to super fast or like and Air bender or something.
- Amon’s voice keeps changing so that is no reason to rule it out.
- Aang could have taught him how to remove bending.
- Amon claimed that he talks to the spirits. “Tenzin is Mr. Spiritual”
- Tarrlock is a pretty obvious choice and wouldn’t be that great of a twist.
- Tenzin is a council member so he would be able to monitor both sides.
- Amon has only taken bending away from criminals so far.
Now, you say what would his motive be? Well, Tenzin is pretty wise. He could have seen that there was a growing divide between non benders and benders. His wife is one of those examples; she wants their next child to be a non bender. In order to assure that there will truly be peace between the two group they must resolve their differences. So, Tenzin has created a rebellion with which he could expose both sides views, and even though there will be some very serious conflict if the people of the world deserve peace they will be able to accomplish it. Remember, War is Peace.