This tale is older then the legend of Nightmare Moon, older than the legend of Discord, even older than Equestria itself.
Over ten thousand years before the return of Nightmare Moon an evil was sealed away and forgotten by all except those that guard its prison.
This tale is of a young filly who's family has recently suffered a terrible loss. And an entity that does not belong to this world. It is a tale of Necromancers and those who seek to destroy them. It is a tale of tragedy.