This is dangerous to write because I'm a bit behind in C3 but I feel relatively safe that The Chained Oblivion isn't a major player in C3. I don't think they're secretly Predathos or the Luxon. (haha watch me be completely wrong lol. If the answer is revealed post C3 ep 86 shhhhh! No spoilers in general, don't be a dick.)
Ok so we know The Chained Oblivion is bound at the bottom of the Abyss by 6 shackles tethered to various points in Exandria. Their locations are a closely guarded internal secret of clergy of the Dawnfather and the Knowing Mistress. We know the location of one in Rexxentrum from C2. My question is, how much do you want to bet one of the shackle's fanes is in Whitestone? lol.
In C1 Matt used to tease them, and us by extension, with the Sun Tree by saying that the Sun Tree may know a LOT of information, but they were asking the wrong questions. That's been in my mind this whole time. What does Matthew McConatree know?!?! Well, the Sun Tree is a tree sacred to The Dawnfather, and rests at the intersection of powerful Ley Lines. The tree was there before the city, in fact, they built the city around the tree. The tree was planted during the Calamity directly over The Knowing Mistresses' Ziggurat temple, and the location of her wounding. We never fully got an answer as to WHY the Sun Tree is there! Is the Sun Tree just watching over the scene of the final battle or is it something more? In fact in C1 ep 70 at (3:10:35) Matt says that Keyleth senses the Ley Lines shoot off in SIX different directions! SIX! The Chained Oblivion is held by SIX chains!!!!!! COINCIDENCE?!?! I THINK NOT!!!! (Ok maybe it is, but still, Matt is ridiculously detailed in his world building, I wouldn't put it past him!)
Whitestone is so fucking cursed. It was messed up long before the Briarwoods got there, they just made it worse. It's where the final battle between The Chained Oblivion, The Knowing Mistress, And The Dawnfather started, The Ziggurat was her temple before it was corrupted, it's where she was wounded (I saw a theory somewhere that the raw essence in Whitestone's rock that can be refined into residuum is actually The Knowing Mistress' blood, which is genius, whoever came up with that, I think you are absolutely correct! That's so damn cool! It has SOMETHING to do with their battle, that much is for sure, what else could it be from?)
The battle ended in Gatshadow, so that's another candidate. Gatshadow is cool, and another important place from C1, but if I had to put money on it, I feel like Whitestone is just one of those places that never catches a break lol. Also Percy's family were originally followers of the Dawnfather (if I remember correctly). The city is a Dawnfather leaning city, Vex is a/the champion of the Dawnfather, which I hope C3 subtly develops further if only in the background. I feel like, of those who were war time converts to fight Vecna, Vex would probably take her duties as Champion most seriously especially considering her position in Whitestone and its relation to the Dawnfather. I'd love to see some Champion of the Dawnfather Vex'ahlia in later C3. (Again don't tell me if it happens).
If Gatshadow was super important strategically, you'd think The Dawnfather would have left a Sun Tree there to keep watch. Maybe he did and we just haven't run across it yet? Seems like we would have seen it on our way to fight Umbrasyl but you never know. They should check the Cobalt Soul library and see if there are any other Sun Trees in Exandria or if Whitestone is it. (The Cobalt Soul, who's favored deity is the Knowing Mistress, someone high up there definitely knows where the chain fanes are!) On second though that's probably way too obvious, having a Sun Tree in each location. They should figure out what other powerful symbols/ followers/ creations of The Dawnfather and The Knowing Mistress there are and look for those! Sphinx's and Sun Trees are only the start. This'll totally be important in Campaign 4 or 5 or 27! Matt plays the long game! He's mentioned The Chained Oblivion too many times for it to not come up again eventually. After the shenanigans around the Angel of Iron's cult and Obaan, and Aeor, Cognoza, the Somnovum, The Eyes of Nine, all that Jazz.
With nothing preventing it from influencing people even from the bottom of the Abyss, it'll happen again. So even if it's just an eternal game of whack-a-mole we'll be seeing their influence somewhere, somehow, at some point lol. "No! Bad! Quit influencing mortals from your prison in the Abyss! Bad Eldritch Abomination, the form of which, were I to look upon it, my sanity would melt into a gibbering puddle of goo! Stop That! Stay!