User blog comment:FTWinchester/Darkness as the overall Big Bad/@comment-9249716-20160126223945

Good theory but there are a few problems. Firstly, is that the mark only controlling whoever bears it. As Lucifer was the only angel to bear it, it wouldn't make sense for anyone else to be corrupted when they haven't carried it. Secondly, there's no real confirmation that the Darkness can actually create anything, and given that we've shown that while she can do things like turning water to wine yet suck out souls, there's no real guarantee to whatever claims she can make about creation. Third, given that she was locked away and she didn't even know who death was, she doubtless wouldn't even know who the leviathan's were either. Finally, getting rid of Death, once again, she didn't know who he was as she was locked away which actually puts Death claims into question. Also, because Dean had the mark, it was only shown that the mark powered the First Blade and his body, not any other weapon. And given that the Darkness can be angered easily and is impulsive, it's safe to say that she has no real plan whatsoever. Good theory but full of holes.