Board Thread:General Discussion/@comment-25896389-20151109052100/@comment-27971057-20151109053939

Well they said last season that Merlin battled the Darkness and tethered it to a human soul.. He also created a dagger to control it..

But in this episode it's revealed that the first dark one created the dagger (accidentally) and Merlin didn't really fight the darkness at all. He was actually trapped by the FIRST dark one.

idk but interesting theory :p