An experiement conducted by Twilight Sparkle to determine the existence of parallel realities plunges Equestria and the surrounding kingdoms into a crisis of unprecedented scale. The barrier between universes is ruptured and from it emerges a sinister mirror image of Equestria with thinly veiled intent.
While Celestia and the Mane 6 must deal with the looming threat of war, Princes Luna must face a quite literal nightmare herself.



(Feel free to point out grammatical mistakes. English is my second language and I do not have a beta reader, so I might simply overlook some things.)