Unbridled Darkness (Torghast: Unbridled Darkness - World Event - World of Warcraft) is seasonal torghast power that's very powerful, however it blacks out your screen so you cant avoid stuff on the ground and/or move around without having fear that you will fall off the edge etc.
However if you have Scroll of Storytelling toy from winter veil event (Scroll of Storytelling - Item - World of Warcraft) you can use it in torghast & bypass the dark screen effect