Zuko's move against Azula when he challenged her to an Agni Kai and she refused was a bit unlike his normal motions. While the end of the move was very Northern Shaolin to me, the beginning of the move had a fluidity of motion that I hadn't seen Zuko use before. Even his circular motions in the past had more tension in them. This time the only sort of hardness or tenseness that I sensed in the move was at the very end.

Now, I'm not entirely sure, but I don't know if that move is truly Northern Shaolin (can anyone tell me if it is or isn't?). I know we're not clear on the elemental whip thing, but after seeing the 'wave of fire' move I started thinking about it.

I think it would be particularly interesting to incorporate an opposite discipline into your bending. Northern Shaolin Firebending is an external martial art while Tai Chi Waterbending is an internal one. You could, in theory, be a more balanced bender by being able to incorporate similar motions from your elemental opposite.

And while there isn't proof that can be considered concrete about this, due to the suspicious nature of Zuko's moves, I still believe it. The Guru made it a point to talk about how everyone was connected and the separation of the four elements was an illusion, and Iroh was able to create his redirecting lightning move by studying waterbenders.

So, Iroh's move isn't exactly waterbending, it is based in his study of how they redirect their chi. In a way, isn't that bending outside your element?