Iron Throne is the epitome of power
Long story short, these are incredibly powerful creatures who bonded with Daenerys and will probably determine the war to come.
OK, OK, we were getting to this. So, Daenerys learned to fly the scaly monsters - and used them in a few battles, which terrified her enemies, as they feared she could conquer Westeros as Aegon did.
In Season 7, though, the Night King threw an ice spear at Viserion, killing him.
The Night King then reanimated the fallen dragon’s corpse, which was pretty bad news for everyone, particularly since the dragons can break through the Wall - which was exactly what zombie Viserion did, allowing the Army of the Dead to enter Westeros proper, setting up the show for the big war to come.
That icy, blue-eyed fellow was the first White Walker, who was created when the Children of the Forest, a nonhuman race who originally inhabited Westeros, stabbed one of the First Men with dragonglass thousands of years ago. He now serves as the leader of the White Walkers and their wights. no one knows for sure. All we do know is that the weapons cannot be forged any longer, and there is a finite amount left in the world.
We know of a few Valyrian steel swords floating around the world. There’s Oathkeeper, which Jaime gave to Brienne (who currently possesses it), and Widow’s Wail, which Jaime carries. Jon Snow carries Longclaw, and Sam took Heartsbane from his family home before setting out for the Citadel. Meanwhile, Arya, carries a dragonglass dagger.
You may remember two full seasons of Arya hanging out with the Faceless Men to learn how to become an assassin. She acquired the right skills but refused to give up her identity, causing her to be essentially disavowed by the other Faceless Men. Somehow, though, she retained her new powers.
In short, Arya can transform into different people. The rules surrounding this aren’t exactly clear, but it’s implied that she can only become people who have died.
Yes, we saw Arya cut the throat of Petyr Baelish aka Littlefinger aka Mr. Chaos Is a Ladder. For what it’s worth, actor Aidan Gillen has said he won’t be appearing in Season 8.
In Season 7, the Night King threw an ice spear at Viserion, killing him.