so i am very curious about amon. (spoilers aplenty)
Some of the stuff you put as spoilers aren't really spoilers like "Amon wears a mask" Also your personal theories aren't really spoilers either.
Yes Amon wearing a mask could mean we have seen him before. However it could mean many other things as well, It could mean he is someone other people in the world would recognize but that we haven't seen because we only have a limited view of the world. Perhaps it's someone Tenzin would know but not us because we don't know everything.
or it could be something more akin to batman "You can kill a man but you can't kill an idea". By creating an alter ego and hiding behind a mask Amon has become MORE than a man. and he has backed that up with unique abilities.
Take V from V for Vendetta for example. He wore a mask the WHOLE movie and we never see who he is. However his guy fawkes mask become a symbol against oppression. In a sense Amon is V, we just are seeing the story from the other side of the fence.
Your next point is spoilerish, so I will sensor some we know that the Bloodbending
slowed him down, So he probably isn't a cyborg, especially since that level of technology is yet to be introduced to this setting. Honestly if Amon is a robot I think Noblebear and I will join forces to decry this series.
In truth it's probably because he is just really powerful spiritually
Also Spirit-bending and Amon are introduced within the first 3 episodes of the series, anything discovered in the first 3 episodes is part of the general knowledge of the series, at least by my standards, just like Tarrlok is a blood bender
may not really need a spoiler tag once we reach season 2 and beyond because the knowledge will reach a critical mass among the fan base and anyone watching the series will likely reach that episode in a short while because they will not be forced to watch them one week at a time as we now are.
While the series has only shown us that only Aang an the Lion turtle have known how to preform spirit bending that does not mean others don't know how to use it. In fact the only reason the lion turtle knew about it was because he was REALLY REALLY old, so anything of sufficient age and wisdom could know about it.
Azhrei has put forth the fact the Koh, the face-stealer could be connected. The more I think about it the more I think I like it. Because we have no information on what the consequences of face stealing are, perhaps it gives Koh the ability to control the physical body. It would also mean that the person's body, with the mind and will of Koh would be a terrible force. Though I personally think this is a bit far fetched and I do believe that face stealing just means you are trapped in Koh, but I would be willing to go along with this.
Of course there was an idea that hit me that we do know something about Spirit bending, From the Lion Turtle we know that Spirit-bending is dangerous and can corrupt and destroy your own soul if perform incorrectly, we also know that it was a technique used BEFORE elemental bending so anyone probably can learn it.
While the anyone can learn it leans more toward Koh, the other part lead to another option
Aang. Amon dodges things with ease like an airbender and he knows spirit-bending, we now know that Aang didn't stop using spirit-bending and seemed to have a sort of arrogance when he took away Yakone's bloodbending
We also know that the Avatar can live lifespans MUCH longer than most.
Perhaps 17 years ago Aang tried to spirit bend someone and his spirit was weak and malleable and it destroyed part of him, turned him into something, in a sens Aang had died and this new person was there, possibly this disrupted the connection to the Avatar spirit and made it move on to the next in the cycle, taking the ability for Aang to bend with it. Perhaps this is why the Spirit of Aang has't tried to communicate more soundly with Korra like Roku did with Aang, because the spirit isn't fully there. Perhaps this is also why Korra has a block from air-bending and contacting the spirit world.It also would explain why Tarrlok would despise being compared to Amon, because Amon is the avatar who harassed his family and took away the power of his father. Amon is a twisted freak of an Avatar who lost the power to bend and is in a sense a different person.
Of course this is just a theory.
An outstanding feat for a fellow cleric to the Wall of Text.
this shit is like a shark, if it stops swimming, it dies.