The King of Hell returns as a regular in Supernatural season 10.
Though we've seen a lot of Mark Sheppard in Supernatural - he's been in 34 episodes since he first appeared in season 5 - he's never been a regular. In fact, Sheppard's never been much of a regular on anything, making brief but memorable guest appearances in shows like The X-Files, Firefly, 24, Battlestar Galactica and Doctor Who. However, we're glad he's settling down with Supernatural for season 10, and not just because he looks great in a suit. (Though it's definitely partially because he looks great in a suit.) While this doesn't necessarily mean we'll see Sheppard's Crowley in every episode, we're certain to see him on more than just special occasions - a sure sign that Crowley's key to season 10's plot, though that was a bit of a given considering how season 9 wrapped up.
Returning as a regular character in season 10 is Misha Collins, playing Castiel who's an angel... or a human angel... or, well, we can't keep track anymore, but Collins is always an entertaining addition to the Supernatural lineup. No word yet on whether Felicia Day will be continuing her role as Charlie this season, but we live in hope.
Source: A.V. Club