Episode 10×16 or “The One With The Nuns”
So far this season: Dean’s been cured from demonism; Crowley was his BFF; Cas was losing his grace until Crowley saved him; and Sam has done his best to reign in Dean’s homicidal tendencies. Claire Novak has also reappeared and swears she doesn’t need a father figure. Cain has confirmed that there is no cure for the Mark. And Crowley has a mother? Spoilers ahead.