Supernatural Season 10 Spoilers: Castiel's Mission, Abel and 200th Episode

Supernatural reaches two milestones in the coming year, as the long-running CW series will reach Season 10 and its landmark 200^th episode. The early portion of the season will likely focus on Demon Dean (Jensen Ackles) and Sam's (Jared Padalecki) hunt for him, but Castiel (Misha Collins) and others are in the mix, as well.

The "Spoiler Room" column at EW.com spoke to Collins and showrunner Jeremy Carver and discovered two reasons why Castiel and Sam are not actively working together to find Dean. Firstly, Collins said Cas, who is dealing with the problem of the grace inside him burning out and slowly killing him, is "not actively trying to fix himself" when Season 10 picks up.

"Cas is resigned to his fate," Collins said. "He's definitely more interested in fixing Dean, and I think there's a bit of a martyr in Castiel, but there's also an unwillingness to cut another angel's throat and steal his grace. He seems to be steadfastly resolute in his determination not do that."

Carver then partly explained why Cas is not working with Sam. "There's more than one reason that Castiel and Sam are not together on the search for Dean at the beginning of the season," he said. "One has to do with Castiel not wanting to be a distraction with his own issue, and then there's another reason which we learn during the episode."

Last season, Supernatural introduced Cain (Timothy Omundson) and the Mark of Cain, which had far-reaching implications in helping turn Dean into a demon. Carver told EW that he would love to bring back the character and the actor, but Omundson is busy with an upcoming ABC show, Galavant, which premieres mid-season.

However, the writers have talked about bringing in Cain's brother, Abel. "That's a great idea, and [it] has been bandied about in the writers room," Carver said. "You know, it's funny. I teased some characters...that have been spoken of but not seen [on the show], and from what I've seen-I don't check it out too much-[the guesses] have been incorrect."

Finally, Kansas' "Carry on Wayward Son," the show's unofficial theme song, will appear in the show's milestone 200^th episode, which Carver described as "musical-ish" during the Supernatural Comic-Con panel.

"Will 'Carry on My Wayward Son' be involved? How do I answer this? I can say, sure. There will be 'Carry On My Wayward Son' in one form or another," he said. "There it is. There's your spoiler."

Carver also revealed fans will see many of their favorite characters from the series represented in the 200^th episode in one form or another. Thus far, all we really know is that the episode has something to do with Chuck's books. Does this mean Rob Benedict could return as Chuck/God?

What are you most excited about for Season 10 of Supernatural? Let us know in the comments below.