SO YOU GUYS - when BC is talking about his siblings in ACOWAR, he mentions “Koschei, too—confined and bound by his little lake on the continent.” ACOWAR pg 239
And I remembered - in Heir of Fire, Aelin and Rowan run into that lake critter when they’re training. LET’S JUST REVISIT THOSE DESCRIPTIONS
1) “It was swimming toward them, lazily. Curious. As it neared, she could make out a snaking body as pale as the stones on the bottom of the lake. She’d never seen anything so huge, so ancient, and—and there was only a thin layer of ice keeping her separated from it….She swallowed her shout as a scaled, massive head stared up at her. Not a dragon or a wyvern, not a serpent or a fish, but something in between. It was missing an eye, the flesh scarred around the empty socket. What in hell had done that? Was there something worse down there, swimming at the belly of the mountain?” HoFp. 287
2) “What the fool learned that night was this: the creature was almost as old as the mountain itself. It claimed to have been born in another world, but had slipped into this one when the gods were looking elsewhere. It had preyed upon Fae and humans until a mighty Fae warrior challenged it. And before the warrior was through, he carved one of the creature’s eyes out—for spite or sport—and cursed the beast, so that as long as that mountain stood, the creature would be forced to live beneath it.” ….
A monster from another realm. Had it been let in during the Valg wars, when demons had opened and closed portals to another world at will? How many of the horrific creatures that dwelled in this land were only here because of those long-ago battles over the Wyrdkeys?
“So it has dwelled in the labyrinth of underwater caves under the mountain. It has no name—for it forgot what it was called long ago, and those who meet it do not return home.” HoF p. 563
THIS IS POSSIBLY PROOF THAT THE THRONE OF GLASS SERIES AND THE ACOTAR SERIES TAKE PLACE IN THE SAME WORLD DURING DIFFERENT TIMES
…or that SJM likes critters trapped in lakes.