[S7] The abilities and motivations of the Others

The Night King may be able to animate the Wights on the other side of The Wall by viewing the corpses through the Weirwoods. Zombro Benjen brought Bran and Meera to a Weirwood not far from The Wall within the Haunted Forest, and from what I recall there is a Weirwood at Castle Black as well.

The Night King may be able to disrupt or dispel the magic that stops Wights from crossing The Wall and the Cave of the Three-Eyed Raven as seen in the assault on the cave. If the Others built The Wall, it would make sense for them to keep contingencies in place.

The Night King may be able to turn the Wights on and off, which would explain the assault on Jeor Mormont and the single Wight captured by Jon Snow and the Bros that was acting very un-White-like for the Others' trap. If this is the case, The Great Other may indeed exist, a shared consciousness between the White Walkers.

Perhaps the original pact with The Others after The Long Night involved sending criminals and outcasts North of The Wall to serve as sacrifices/replenish the White Walkers' ranks. Over time, too many were sent, and they banded together as the Wildlings' clans. The oaths were corrupted eventually, and the criminals were sent to serve as Crows. With the lack of sacrifices, the Others realized that those North of The Wall were born there and not sacrificed, then decided that the pact was broken, and prepared for war.

Apparently, the Night King sought out steel chains over the millennia just to drag Viserion out of the frozen lake. The Free Folk have little knowledge of metallurgy beyond the Thenns, who can forge bronze. He would somehow need to secure huge steel chains over the ages, knowing that he would be capturing a dragon in the exact way that he did. If Azor Ahai was actually a dragon rider, and his labors to create Lightbringer were in actuality attempts to hatch an egg, that would explain why The Night Man plotted and waited for so long to have dragons at his own disposal, without there being too many to successfully combat.