Apollyon’s Vampires
Circa 9,450 DCE
When the divine returned to the material plane, Apollyon found the tieflings worshiping Devils and Demons, and they refused to return. In his anger he cursed/blessed a small few who did return to him, along with some Drow and mortals that now inhabited the lands after fleeing the prime plane.
This blessing turned them into undead, that feast upon the blood and lives of other mortals, and contain great power. Feasting on mortals would transform them into thralls for the vampires, and feeding the thrall it’s blood would transform them. Each generation would grow slightly weaker, but each generation that weakness would lessen until it was indistinguishable.