"The French Mistake"

Raphael launches an attack on Castiel and his allies, sending a particularly frightening angelic hitman after Balthazar, Sam and Dean. In an effort to protect the brothers, Balthazar sends them to an alternate universe where they are the stars of a TV show called "Supernatural" and they are actors named "Jensen Ackles" and "Jared Padalecki." The brothers are confused when Castiel appears to be a tweet-happy actor named Misha Collins and Sam is married to Ruby.

Of course today's much anticipated Supernatural was written by Ben Edlund.