episode one - to save Sam, Dean lets angel Zeke possess Sam (incidentally in this episode Hael wants to possess Cas)
episode two - Dean confronts Abbadon who wants to possess him, Zeke saves Dean
episode three - Dean stabs April who killed Cas, Zeke saves Cas, but Dean has to send Cas away, in this episode are angels possessing humans.
episode four - Dean and Sam are possessed by the Wicked Witch from Oz, Zeke saves Charlie, implying this should make us (the viewers) trust him.
episode five - While on a case, Dean becomes dog-like
episode six - Dean and Cas work a case, bond momentarily but Dean has to send Cas away
episode seven - Dean returns to a foster home where he spent time before he rejoined hunting for Sam.
episode eight - Dean and Sam sign a chastity pledge so that Vesta can eat them. Sam gets a clue that he is possessed
episode nine - Dean and Sam meet Cas, but Dean has to send Cas away, Dean tries to get Zeke/Gadreel away from Sam, Gadreel kills Kevin and leaves the bunker possessing Sam.
episode ten - Cas, Dean and Crowley get Gadreel out of Sam. Sam is mad at Dean, Dean blames himself for Kevin (and Sam) and instead of sending Cas away, Dean leaves the bunker.
episode eleven - Dean and Crowley find Cain, and gives his Mark to Dean - who wants to kill Gadreel for revenge for Sam. Meanwhile Cas heals Sam, Sam is still mad at Dean
episode twelve - Dean and Sam find Garth, Dean decides not to kill a monster, Sam is still mad at Dean.
episode thirteen - Sam and Dean go on a hunt, Dean decides not to kill a monster, Sam is still mad at Dean.
episode fourteen - Kevin appears, Dean apologizes to Kevin, Sam and Dean find Linda, Sam is still mad at Dean.
episode fifteen - Dean and Sam meet Ghostfacers Ed and Harry, Sam and Dean share a moment and might get along.
*Carver seems to plan in four episode blocks, with first theme being possession, second theme being Dean sacrificing for Sam, four episodes of Dean separating himself from Cas to protect Sam.
see Cas scan of season nine
Sam scan of season nine