Is the big-eyed thing 
fought for the rune a voidborn or a watcher? I ask because on the interactive map it says "Facing the Void" yet in the description it says "... even the mythical Watchers are drawn to the power of the World Runes…". So which is it a voidborn or a watcher? Or is it some amalgamation of both?
It is not a watcher. It is a common misconception, but WAAARGHbobo confirmed it's a regular Voidborn.
It is a watcher. The watchers are now something like rulers of the void but they used to live colse to Frejolor(butchered). Thats the new lore apparently. It is said in the Ichatian story as far as I remember. Everything from the Kai'Sa release can help you. And from the recent Darkin stuff I guess. But as far as I see you haven't read much of the new lore. I don't blame you but if you want to be up to date you have a lot of reading.
Edit: There is always good old Necrit of course. The map can help you too. Ichatia is in the right hand low corner of the Shuriman continet. There is all void stuff that may interest you.
