A trip to an alternate dimension leads to the peak meta brilliance that is "The French Mistake." There's not actually a monster in this monster-of-the-week episode, but it still counts because Sam and Dean go where they've never gone before: to a world where Supernatural is just a TV show. Ultimately, this episode is basically just an excuse for the actors to make fun of themselves (Misha Collins is definitely the MVP), but it can't be overstated just how delightful "The French Mistake" is to watch.