Long read, but this is why I think this is a final battle or maybe important future battle between main characters of the show and the Night King. I thought it was a WW at first too. There's a shot of a dead horse and in the top right you can see the same hand with the sane lance. The horse looks exactly like Coldhands' horse. If you look at the "wights" none are bone. All look very human and the red haired, shirtless woman with the axe looks alive. Front left you see a small persons head(Tyrion?). The body blocking his looks like Jon holding Longclaw. The bald guy may be Varys. I don't know who that is between Tyrion and Varys. Shirtless woman is Sansa. Right side, right next to the rider is Samwell with a bow. Behind him is Arya. I don't know who the other two are but one may be Torrhen(sp?) Redbeard(The wildling leader). Notice two silhouettes on top of the wall/mountain? In the next shot you see a horde of Wights and WW's approaching the same wall/mountain. In that shot the wights are clearly dead/bones and the WW's are all(and always depicted) wearing armor. There are no silhouettes on top of the mountain. I also find interesting that there are 7 people besides the rider. They are all cloaked and clothed. They all walk upright and there attention is to the silhouettes on the wall/mountain. Also note the guy in the bottom right corner appears to be holding a blunt weapon, which the WW's/Wights do not use. In the close up shot of the horse, you see the rider's hand holding the lance, and the lance and his hand appear to have a glow. The next shot shows the Night King, I believe to show the contrast and differences between the rider and the Night King.