So, as the writers have been giving small little bios to skins(which I deeply appreciate), I've noticed that for the bios of Nottingham Ezreal, Viridian Kayle, and Blackthorn Morgana all make direct mentions of Elves. What I want to know is if they're all part of the same universe, and if so, is it one we already know or is it one that will have more thought put into down the line? Personally, I'm sort of an Elf fanatic, so, I'm all for more Elves and Elf skins.
From what I've gathered so far, mostly from the bios of Viridian Kayle and Blackthorn Morgana, the Elves once had a powerful kingdom built on the foundations of magic, that as Blackthorn states, "evil power that some once considered the cornerstone of their magical supremacy." In Viridain's bio, it mentions that for those who can find some of the ancient Elven magic "are gifted with incredible power over the natural world." If "over the natural world" is anything to go off of, it could be assumed that their magic is less arcane and more primordial, stemming from the world itself rather than from some well of magic or other outside source. From both of their bios, we discover that the Elves since the time of the ancient empires have split into two groups, the Forest Elves and the Dark Forest Elves, the Forest Elves living alongside humanity while the Dark Forest Elves remain in their ancient homes, guarding whatever magic is left of the old empire. However, the Forest Elves are also known to go exploring for remnants of their lost civilization.
With little to go on, and just my imagination, my theory is that ancient elven empires were your typical over controlling evil fantasy empire, and the original descendants of the Forest Elves were those who rebelled against it. Once the empire fell, the split was between those who were willing to live alongside humanity, and those who weren't. This is just a side note, but I think it can be safely assumed that Nottingham Ezreal is a Forest Elf and not a Dark Forest Elf.
However, none of this answers the question of what skin universe they belong to.
My guesses would be either Dragon World or Elderwood/Coven skinlines, just because they're the only fantasy themed skin lines with a flushed out story and background.