User blog comment:KillRoy231/Mary and Lucifer to return/@comment-10889355-20170620051110/@comment-1031724-20170622053831

They reformed the Darkness, who was the purest Dark Form imaginable, and the origin of the devil's evil (though Lucifer stayed evil after losing the Mark of Cain).

Right now she and Lucifer are the only two main villains left alive, even though Metatron, Rowena, and Crowley reformed before death.