How would you go about boiling down a much-loved setting into a one-shot, or a movie - or a Twilight Zone episode complete with twist ending? Maybe even twice?
What is the big plot you’d pull out and adapt? I can kind of answer this one from experience - having stolen the Big Bad plot from The Watch House season four for Nationals one-shots and the like. (It’s the one where they try to resurrect every vampire ever slain in the nearby area, which obviously get increasingly hazardous the longer a series about killing loads of vampires in a particular town goes on.)
And what is the twist ending? I imagine for Buffy it would be that the Vampire Slayer turns out to be a teenage girl. (Battlestar Galactica starts with the premise of a classic Zone twist, by way of an example.)
The other thought this thread gave me was what would an anthology series about your setting be like? A new cast, a new location, even a new time period, but all in the same setting. For Buffy again, we have Tales Of The Slayers and Tales Of The Vampires, collected short comics stories (and text stories) about, well, you can probably guess, throughout history. A one-shot adventure offering a different view of your regular setting could be very interesting.