Adam Milligan return / Archangel team up
It's been 5 years since we last saw Adam who had the unfortunance of falling into the pit and possessed by Michael and currently remains there. It has been theorised that Adam has been tortured by Michael and Lucifer this whole time, but I don't think so as Micheal must know that if he ever gets out he needs a vessel of Winchester bloodline and Adam is the only living member of the family that said yes so he'd need Adam and he wouldn't exactly say yes again if he was being tortured.
Through a series of events some supernatural entity should gather the horsemen rings, Sam and Dean have 3 of them still and now that Death is dead I assume they will take possession of the last one. Now with the Darkness itself upon the Earth, a force that not …