The watchers are referred to several times in the lore. I might have missed something while going through the Freljord lore but I'm not sure what exactly the watchers are.
Are they powerful beings corrupted by whatever corrupts Lissandra?
Or are they something else?
We dont know a lot about them , but we know that they look like 
and that they are the original power of Freljord's ice : They gave Power to 
and her 2 sister Avarosa & Serylda , 
&
are the descandants of Avarosa and Serylda so they have the same power , Avarosa defeated all the watchers in war , so killed her traitor sister and she is waiting for the watchers return from centuries . Thats all we know x(
