User blog comment:Zathronas/Analysis by an author: Part 2 Antagonist, the Darkness/@comment-10380701-20131216235749

This sorta fits into the Mother Grimm theory. From what I remember, there's what's best described as a god that rules the darker side of Remnant, and it's the one creating the Grimm.

The Darkness is the Mother Grimm.

Of course, this only works if the Darkness was a singular entity. If it's not, then that's where both theories differ.