The recent events in bloodbending has everyone making speculations. I was not surprised that we would find this eventually, but I did not think it all would happen so soon. I figured they would be more gradual about it. The biggest controversy was how bloodbenders could do just that without a full moon. I had made several theories about it months before purely for fun, but I didn't think they would become canon (or at least not so soon). But to figure that out, we need to know what the full moon provides the bloodbender that they wouldn't normally have. I theorized that only powerful waterbenders would be able to bloodbend, but even powerful waterbenders still needed the full moon because of what it provides so that they can overcome the natural resistance (whatever that may be) of animals. So what do we know about the full moon?
1. We know the moon makes waterbenders stronger, and the full moon does this much more drastically than any other phase.
2. The full moon may provide a spiritual element that even 99% moon can't give. The moon has to be completely full in order for this to work. This one is just possible not proven. It may not be true.
- So if a powerful waterbender could find a way to increase their power enough, it might be possible to bloodbend without a full moon. That was unless there had also been some spiritual aspect to the full moon that couldn't be replaced/replicated, but that wouldn't be any fun. ;) So I made my theories anyways. And because we now know they can bend without the full moon, we know that the full moon provides nothing that can't be replaced. I had many theories, but I'm only going to give my best one because that one turned out to match the events in the show almost perfectly. Well, at least it matched up well from a logic standpoint.
The major theory:
So my major idea was using the chakra gates like Guru Pathik did to increase the power and flow of the benders natural life force or chi. As the life force inside humans, chi would also have a spiritual element to it that would effect more than just the power of a bender. It doesn't just effect the Avatar and the Avatar State, but can positively effect benders and even non benders. Pathik wasn't even a bender. But this allowed him to do things like live a long time, and know about metal being linked to earthbending before Toph discovered how to do it.
This might allow the bloodbender's chi to overpower the chi in another animal's/human's body. And it might allow the bloodbender to do so without needing assistance from the full moon, due to the now heightened state of their chi. The chi theory is especially likely for waterbenders, because we know they already manipulate chi flow as that is how they heal.
It would also explain why Amon was able to resist it, if Amon also had increased his chi level with this technique or something similar. It is worth a mention, that Aang's Avatar state was likely able to overcome bloodbending for the same reason. By increasing the power and effectiveness of his chi flow with the Avatar State, he was able to push out the chi that would control the water in his body from within and therefore resist bloodbending, or simply overpower Yakone's control of Aang's own chi to bloodbend him by creating a powerful surge of chi flow. I believe Amon used a similar method, but obviously without the Avatar State.
However the actual specifics of it turn out to be, this explains how Yakone and Tarrlok can bloodbend without a full moon, and how Amon and Aang were able to resist it. Again to be clear, Amon's technique was different than Aang's because it did not involve the Avatar State. While the Avatar State works well for this, it isn't required for the same method. Anyone (including non benders) can increase their chi flow this way, and so a bloodbending resistance technique like this would be possible even for non benders.