Mephisto, Lord of Hatred. Baal, Lord of Destruction. Diablo, Lord of Terror.

The three Prime Evils that long ago invaded Equestria in a vicious and bloody rampage. Brought to heel by the efforts of the Horadrim, who now protect the mortal world. Centuries the Prime Evils have lain dormant. But now… The stars portend a coming cataclysm.