Cass, now juiced up with all the souls of purgatory compels Bobby, Sam, and Dean to bow before him or be destroyed. When they comply he says they only do it out of fear, not love or respect and offers to let them live if they don't get in his way. While Cass cleanses his "followers" and smites the angels who opposed him in Raphael's rebellion the brothers try to figure out a way to beat down Cass. They figure that Death is the only person who can kill Cass and Crowley, now indentured to Cass, gives them a spell to bind Death. They get a lightning struck piece of sand that is an "Act of God" frozen and bind Death and Cass shows up who unbinds Death before he gets killed. Death warns Castiel that there aren't just souls in purgatory and that the Leviathans are in there with him and that Purgatory was created to keep them in. As ever Supernatural expands its own mythos even further giving it more of a supreme purpose. When Sam experiences hallucinations of his time in Hell now that the Wall's down in his head, Lucifer appears to him and tells him that he never left the cage but that's obviously not true in this case and he disappears right as Cass approaches the brothers to put the souls back into purgatory.When the souls go back Cass promises to redeem himself but Cass says that the Leviathans held on inside of him and they kill him and take over his host. With a declaration of "This is going to be fun" and the celebratory throw the main characters around the room trick that Supernatural loves to do we are in the same situation and location we were an episode ago just with new villains. Now that we have a solid baddy going straight into the season this could be some really good stuff to come. Dean's unwillingness to forgive Cass is understandable now that he's been bitten way too many times. Maybe the Leviathans will split off and wreak havoc as individuals to give them a season long arc of fighting against for the brothers. Goodbye Castiel, it was good knowing you. His 180 turn was satisfying and that the writers didn't back down from his arrogance was a tour de force and of course the consequences are there plainly to be seen. Hopefully Season 7 will continue to deliver prime episode real estate for all.