I find all the rationalising of poor plotting/attention to detail hilarious.
It's not because the plot has holes guys.. it's because the Night King sees all!
Not that I necessarily disagree with the theory that the Night King might be a greenseer, but trying to make all the bits and pieces fit into the plot is also quite silly.
Here's how I think the final season plays out. I could be completely off the mark but here goes...
Spoiler
First off I'm starting to get pretty sold on theories about Bran being the Night King. Or more specifically, Bran going back in time and warging into the guy who we saw the Children of the Forest turn into the Night King. Bran has been warned by the previous three eyed raven about getting 'stuck' when travelling back in time, and I think he gets stuck as the Night King for the thousands of years leading up to the present events.
I think in the final season the Night King will really start kicking arse and clearly be winning the war. That will make Bran go back in time to try and kill him before he gets so powerful (when he didn't have an ice dragon, such a huge army, more white walkers etc).
This first attempt will be contacting the Mad King Aerys, who still had control of the seven kingdoms, and could go north of the wall to 'burn' him (leading to him going crazy and wanting to burn King's Landing instead).
When this doesn't work and things get more desperate, he decides to go back to convince the Children of the Forest never to create the Night King. He controls the human pre-Night King to plead with them, but they don't listen and turn him anyway, leading to a few thousand years of Bran being trapped.
As for the bittersweet ending George R.R. Martin talks about, I think that Jon (Azor Ahai) learns that Bran = Night King and that Bran must be killed for the Night King to die (I imagine a scene where Valyrian steel or dragon fire has no effect on the Night King because Bran is alive). Jon could find out by Bran taking him back in time as well, or Jon could be shown it in the fire by the Lord of Light.
In true Ned Stark fashion (he who passes the sentence swings the sword), Jon kills Bran to end the war...
Also, are you reddit user
turm0il26 by any chance, mate? Because you both seem to have arrived at similar theories.
"Bran goes back all the way to where the Night king was created, to warg into the human that later is going to become the Night king. He wargs into him to instead stop the 'dragonglass into the heart'-event from happening. Only he doesn't think of that the children of the forest won't recognise him from the future, and that they at that point are in war with the first men (he is gagged because of all the weird future-talk). When he realised he failed again, he tries to go back in the current timeline, but can't because he's too deep into the past and stayed too long ('it is beautiful beneath the sea, stay too long and you drown'). From here Bran gets stuck in the past (exactly as Brynden and Jojen warned him not to) and becomes the Night King."
I also find the idea that with the power to warg into absolutely anything, Bran chose to warg into not one of the children of the forest.. but
the guy he knew the children were going to turn into the Night King somewhat amusing. I mean, you know the guy is going to be turned into the Night King and your play is to use
that guy to tell the children that you're going to turn into an omnipotent killing machine that threatens the existence of all man/children kind. Word?