Discord warns the citizens of Equestria and the rest of the planet of the coming of the Imperium and their Inquisition. Horribly outmatched, they accept a deal with the devil they've befriended, and are changed forever. When the Inquisition DOES come, they will find that the helpless planet of Harmony they were expecting to cull has changed, and the face of the Imperium will be changed forever...

Author's Note: An idea that came to me recently. Updates will be very slow, as I need to learn more about the 40k universe.