Abigail Raney writes for Bleeding Cool:
I'd say most of what you need to know about where season ten of Supernatural picks up can be encapsulated in the brief teaser that was offered at their panel. Sam and "demon Dean" are squaring off, and Dean throws out the accusation, "I know what you did when you were looking for me. I know how far you went. So let me ask you, which one of us is really the monster?" And then he comes after Sam with an axe, proving that just because you have a point doesn't mean you're not out to murder someone.
Beyond pondering the age old question of whether or not humanity really has any moral superiority over the forces of darkness, the tenth season will find Castiel with his powers fading, though actor Misha Collins says Castiel's priorities are in helping Dean. Collins also joked that he wasn't worried about the presence of a Constatine TV show threatening the heavily inspired-by-Constantine Castiel, because now Supernatural has "squatter's rights" on the character's look.
Mark Sheppard, who will become a series regular in the tenth season, surmised that what the audience would learn about Crowley this season is that "he's always right" – which Jensen Ackles somewhat countered by voicing his own opinion that eventually Crowley will hit a turning point with demon Dean and start thinking, "This was a bad idea."
The cast gave a few hints about the 200th episode, which apparently will be "musical-ish". Ackles threw out the tease, "Apparently, demon Dean likes to karaoke – or doesn't. I don't know." But executive producer Jeremy Carver stressed that even more important than the musical aspect of the 200th episode will be the fact that it's a "love letter to the fans".
In response to a fan question about more permanent female characters on the show, Carver promised season ten will have a "very healthy dose of new and returning female characters". Former cast member Osric Chau, who played Kevin Tran, came up to the mike in costume and then revealed his identity in order to query whether Kevin would ever return. "Not now," Carver quipped.
As for whether or not William Shatner, who often live tweets the show, would be welcome as a guest star at some point, the answer, in keeping with the tongue-in-cheek tone of the rest of the panel, was of course – but "he'd have to audition like everybody else." We'll be watching Shatner's twitter to see if he accepts the offer.