Of all the villains on Game of Thrones, the Night King is by far the most unsettling. While we can at least understand the complex motives and backstories of the human baddies, the Night King is single-minded in a quest simply for an endless night. Not only that, but he has a pretty terrifying set of powers that can make even the most fearsome human warriors quake. Here's what we know about what the Night King can do.
The Night King was, as seen by Bran Stark in one of his many visions, just an ordinary man among the First Men, before being captured by the Children of the Forest and forcibly turned into the first White Walker by being stabbed with dragonglass. The White Walkers were supposedly created to defend against the invading First Men, but eventually turned on their creators and overwhelmed them with their power. Those powers include some truly frightening ones, such as the ability to make more wights, as well as battle-ready abilities that make him nearly invincible.
On a basic level, the Night King has superhuman strength. Although he hasn't been seen in hand-to-hand combat yet, he was able to throw a spear over a mile with enough speed, accuracy, and force to mortally wound the dragon Viserion. He's also apparently resistant to fire, which is a tried and true method of dealing with some White Walkers. Instead of being destroyed by it, he can walk through it unscathed. That magical chill also extends to being impervious to normal metal weapons; they simply shatter on contact rather than doing any damage.
That's just the tip of the iceberg, though (pun intended), when it comes to the horrifying things the Night King can do. He's apparently able to ride a (wight) dragon, for complicated reasons. He can raise the dead, reanimating corpses into more White Walkers, and he can turn someone into a wight just by touching them. Even creepier: his "touch" can mark someone, too, making it so that no physical or magical barrier can prevent him from finding them; that's what he's done with Bran Stark. It's possible that he can sense warging, too, but it's unclear if that applies to everyone who can warg, or just to Bran because he's been marked. The long and short of it? It's going to take a truly herculean effort to defeat the Night King, if it's even possible at all.