On Castiel: He’s another brother, or, he’s another main character. That creates different stories, that’s created a very interesting arc for Season 6.
On Misha: The way he interprets that character, there’s a quotient of autism in it. He’s got a very nice grasp on a sort of nonhuman delivery, but it’s very endearing…Misha is one of those guys with a huge amount of enthusiasm. He’s someone who thinks into what’s gonna come up and he wants to add to it. It’s just a really good combination, Supernatural and Misha Collins.
– Ben Edlund (S6 Blu-ray Extra)