It's been a dozen centuries since Discord's cousin Hades sold his former realm of Tartarus to Celestia and Luna, and now he's decided to get back into the game with another realm, a lighter, fluffier realm of daydreams that he calls Mythos. Visiting Rainbow Dash on Nightmare Night to recruit her as a professional daydreamer, Hades sets eyes on Fluttershy, and, well, a myth's gotta do what a myth's gotta do...
This story wasn't actually an entry in the Flutterdash group's Nightmare Night Story Contest, but it was inspired by the prompt.