Shadow elves are the only ancestry borne of the magic if three gods from three seperate periods. Originally, they were simply wode elves or high elves when the Arcfey created them, nothing overtly special about them. Then the Lady of Arachnids slowly wove a cocoon of corruption over a small collection of these elves. Seeding in this chaos to create a mortal army during the War of the Gods, and her plan was successful. But following the Ritual of Separation, these elves were driven deep underground, into the Dark Maze, where other banished beings were sent.
It's there that for millenia they lived, changing and evolving to live in this world. But, from afar, another divine being attempts to heal this corruption as a favour to the leader of her sect. The Dead Flower slowly rotting away this malignant influence, creating a small subset of shadow elves who returned to their worship of the Arcfey, and an even smaller one who instead worship her. Leaving the Dark Maze and even Consarcio to instead serve as her mortal hands on the plane of Shadow.