This article is about the shared universe created by Alicia McKenzie. See Shadowland for other uses.
|See also:||shared universe, multiverse|
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Shadowlands is a shared universe created by Alicia McKenzie in the X-Men fandom that has since spread slightly into other fandoms, including Buffy and X-Files. The "main" storyline of Shadowlands is known as The Oasis, but stories outside of this timeline featuring a wide variety of X-Men characters have also been archived at the Shadowlands archive.
The main concept behind Shadowlands is that after the events of The Twelve, reality has been torn apart at the seams and everything is constantly shifting and converging, causing "time" as a linear concept to cease existing. The entire multiverse now exists in a single place and The Twelve begin to merge with their alternate selves, becoming aware that the resultant chaos is their fault and slowly descending into madness even though they hold the key to fixing the problem. The summary for Shadowlands as a universe, listed above the stories in the archive, is as follows:
What happens to your life when, in a blink of an eye, another timeline can crash into yours and carry you away with it? How do you live, when every step leads you into another world, farther and farther away from the places you knew and the people you loved? When the living give way to the dead, when the dead give way to emptiness, what sort of existence is left?
Do you give up?
Do you fight back? 
The original Shadowlands fic was Aspect, which dealt with Cable and Wolverine in the aftermath of the multiverse converging. When later reflecting on the inspiration for both "Aspect" and the whole concept of Shadowlands, Alicia would cite Adventures of Luther Arkwright by Bryan Talbot and Vanishing Point by Michaela Roessner. The history that led up to the creation of the Shadowlands archive is murky, like so much of early online fandom where mailing lists no longer exist and websites have shuttered, but eventually people began to write fic based upon Alicia's original story and the archive was created on Comicfic.net where the rest of her fic was already being archived.
By that point, Shadowlands was well-known enough to be included as a term on "The Fandom Glossary" with the following definition:
A genre created by Alicia McKenzie in which the culmination of the X-Men's "Twelve" plotline resulted not in Cyclops' death but in a shattering of the walls between realities, resulting in a deadly patchwork multiverse where anything can happen as the shards of possibilities drift randomly. Mainly a comic-book genre but by its very nature is expanding into others, ie. Buffy and X-Files.