1,500 years ago, Celestia and Luna led the ponies of Equestria in a war against Discord and his allies, the Diamond Dogs, who sought to rule Equestria. At the height of the war, they found the Elements of Harmony, and sealed away Discord, and the leaders of the Diamond Dogs, the Twelve Arcana and their master, who the princesses only knew as Diamond.

Now though, prisons are breaking and spells are failing, unleashing many old threats upon modern Equestria. Including Diamond and his Dogs.