1) Once More, With Feeling – Season 6, Episode 7
The total reverse of “The Body” in the fun factor is “Once More, With Feeling” AKA the musical episode. Joss Whedon had always intended to do one since creating the series, and he finally rose to the challenge in season 6, where it provided a welcome spot of light in a very dark run. Not only that, but it’s probably the best episode of the whole show.
Far from being a lightweight outing where the cast get to dance about and sing some songs, “Once More, With Feeling” is clearly made with more care and love than just about any other episode. Whedon uses the structure of the musical to reveal the inner turmoil of each of the characters, with several damaging lies coming out by the episode’s end. And its all done with some incredibly catchy songs songs that sport emotive, hilarious and multi-layered lyrics.
Though it wasn’t the very first musical special of a TV show, it’s roaring success surely inspired the trend for them that followed – e.g. The Flash is about to attempt one very soon. None of them, though, have come close to matching the heights that Buffy the Vampire Slayer did.