Buffy Summers has just clawed herself out of a coffin. Her vision is blurred, ears ringing, hands bloodied, body trembling. She is back in Sunnydale, but something is amiss: The town is overrun with demon bikers, and the streets are ablaze. Someone who looks exactly like her has been drawn and quartered, but the body is a robot version of herself. After dispatching a group of bloodthirsty demon bikers, Buffy sees the same tower where she plunged to her death to save the world in the previous season. The visions of that night come back to her. Just as she’s about to jump from the tower again in an attempt to end her waking nightmare, Dawn begs her sister to turn around and talk to her. Finally, Buffy speaks: “Is this hell?”

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If there is one moment that encapsulates the much-debated sixth season of Buffy the Vampire Slayer, it’s those first words that come out of Buffy’s mouth in the season premiere, which first aired on October 2, 2001. It wasn’t hell, by the way, but for fans accustomed to series creator Joss Whedon’s delicate balance between snappy one-liners and spells of pathos, the hard left into a relentlessly bleak season might as well have been. A resurrected Buffy aimlessly languishes in her responsibilities as the Slayer while working at Sunnydale’s equivalent of a McDonald’s; Buffy’s friend Willow (Alyson Hannigan) struggles with a disconcerting addiction to magic; Spike (James Marsters) tries to repress his romantic feelings for Buffy; and, at the beginning of the season, her mentor Giles (Anthony Stewart Head) leaves Sunnydale for the U.K.

The seventh episode of the season, however, strikes a different chord. Following a brief overture in the Summers household and Giles’s bookstore, Buffy makes her nightly rounds at Sunnydale’s graveyard, the town’s hotspot for supernatural happenings. Then something weird, even by Buffy standards, happens: The Slayer begins to sing.

“Nothing seems to penetrate my heart,” Buffy croons, as a horned demon and vampire question her ambition (“She ain’t got that swing,” the vampire chimes before knocking her down, to which she replies, “Thanks for noticing”). The number crescendos as Buffy pleads to feel alive once more, her climactic words bursting through the vaporized dust of a final vampire being staked in the chest. So begins “Once More, With Feeling,” Buffy the Vampire Slayer’s musical episode — the best episode the series ever made, and one that doubled as an inflection point for Season 6 and the title character’s resentments and insecurities.

The setup, which was written and directed by Whedon, was delightfully simple under the pretext of the genre: A stylish demon named Sweet is summoned to Sunnydale, and he forces everyone in town to reveal their innermost secrets and fears in elaborate, impromptu song-and-dance numbers. When townsfolk begin bursting into flame because of rapid and unstoppable dancing (just go with it), the gang realizes that revealing their secrets in song causes far more problems than it solves. For Buffy, this means finally telling her group of friends, the Scoobies, that they didn’t save her from hell, but tore her out of heaven. The Scoobies, meanwhile, perform their own confessions: Xander (Nicholas Brendon) and Anya (Emma Caulfield) go full Fred Astaire–and–Ginger Rogers in pajamas to admit to reservations about their marriage — a presage to Xander leaving Anya at the altar later in the season. Tara (Amber Benson) sings caringly of being in love with Willow and falling under her spell, later discovering the truth in those words when Willow wiped her mind after a fight. And in the most shocking (and hotly anticipated) turn of events, by the end credits, Buffy and antihero vampire Spike finally release some long-simmering sexual tension by passionately making out as the rest of the gang appropriately sings, “Where do we go from here?”

Fans, however, might’ve been wondering how the hell we got here. Even for Buffy — which was already 100-plus episodes deep and dealt with a litany of supernatural oddities, including a Season 4 episode that went silent — a musical was far outside the norm. But as Whedon explains on the DVD commentary for “Once More, With Feeling,” he’d always wanted to make a musical: “I never had the time, the wherewithal, or the guts to do it before.” Given Buffy’s talented cast — he knew that James Marsters, Anthony Stewart Head, and Amber Benson could sing well — Whedon decided the show would be his best shot of seeing his dream come true. Buffy producer David Solomon said that the episode came together rather quickly. Whedon gave him a tape that Whedon and his then-wife Kai Cole had cowritten and performed during a months-long vacation in Cape Cod. The songs on that tape would eventually become the structure of “Once More, With Feeling.” “The entire thing was him and his wife singing the entire score, and they both played all of the parts. He played all of the male parts, she played all of the female parts,” Solomon said. The tape, which Solomon recalled as being about 36 minutes long, took him by surprise, since he had expected only half of the approximately 42-minute episode to be filled with musical interludes. “It was brilliant. Brilliant. It’s one of the craziest, best things I’ve ever heard in my life. And once I heard it, I knew everything was going to change.”

However, the music was just half the battle. Creating the dance routines was beyond Whedon and the Buffy team’s expertise. Gellar recommended her friend Adam Shankman, a choreographer who had worked on Paul Thomas Anderson’s Boogie Nights and Disney’s Anastasia. (Shankman would go on to choreograph for the first Step Up and the 2007 remake of Hairspray, and also served as a judge on So You Think You Can Dance?) “I was really happily impressed by Joss’s overall sort of vision board, and that he’d written the music,” Shankman said. “You know, that he was so into it. And I couldn’t believe that I’d found such a fun, kindred spirit in terms of loving musicals.”

By Season 6, Whedon was taking a more hands-off approach to the show. Buffy spinoff Angel and the first season of Firefly was also on Whedon’s plate, so executive producer Marti Noxon had taken over as Buffy’s showrunner. But this episode was more of a personal effort than most for Whedon, and he took the time to make sure things fit into his vision. “Joss had a lot of fast references for me, and I knew how to respond to that sort of thing,” Shankman said. “He would come to rehearsals, and say, ‘I like this, I don’t like this,’ and you just make adjustments.”

Still, churning out a musical in the middle of a TV season was arduous. Buffy was treated like a network procedural in its heyday — back before the age of streaming and Peak TV, back when 22-to-24-episode-order seasons were still the norm. (Six of Buffy’s seven seasons, including Season 6, were 22 episodes.) This heavy load meant quick turnarounds between filming the episodes: A typical Buffy show was completed in about a week. “Once More, With Feeling” came with its own additional challenges: The cast needed to learn dance moves, and certain actors needed to become comfortable enough to sing, before spending extra time recording the episode’s music in a studio. “Most of them were nervous about it,” Solomon said. “Not because they couldn’t sing, but nobody had heard them sing and everybody’s always a little uncomfortable. They’re not professional singers in any way.”

“I knew because of the consolidated schedule that I was just going to have to adjust anything to what their abilities were,” Shankman said, explaining the cast’s reservations about the dance routines. “So if there was something they couldn’t do, we just didn’t do it.” Alyson Hannigan “begged me on her knees to have her sing as little as possible,” Whedon said in the DVD commentary. In the episode, Hannigan has just two lines — one of them is, knowingly, “I think this line’s mostly filler.”

Other cast members, however, were more game: Gellar was initially hesitant to do the singing herself, but after reading the script and recognizing the episode’s importance to Buffy’s arc — with its reveal that she had been expelled from heaven and her starting a fling with Spike — the actress changed her tune. “I really went back and forth to whether or not I was going to sing,” Gellar told Entertainment Weekly in 2017. “And Joss said, ‘I’ll do whatever I can to make it as easy on you as possible,’ like bringing in my friend Adam Shankman. But it was exhausting.” The process of singing and dancing in such a tight schedule, however, was so demanding that Gellar then requested a brief break from the show. The 11th episode of the season, “Gone,” in which Buffy vanishes thanks to an invisibility ray, was conceived by writer-producer David Fury to give Gellar a much-deserved breather.

For the role of the show-stopping demon, Buffy dipped into the Broadway talent pool, picking up three-time Tony winner Hinton Battle as the cocksure, beguiling Sweet, who assumes he was summoned to Sunnydale by Buffy’s little sister Dawn, and plans to take her away as his child bride. (Fear not, the episode acknowledges that this is very creepy!) Battle is barely recognizable under heavy red prosthetics — the demon’s face is full of weird curvatures, and he has a gem on his forehead resembling an Infinity Stone. In a showy entrance, Sweet introduces himself to his presumed bride-to-be by tap dancing and changing the color of his suit midsong, with a silky tenor that makes him perhaps the only remotely attractive non-vampire monster in the show’s history. “Bringing in somebody like [Battle] was really, really fun,” Shankman said. “It all moved pretty smoothly.”

The Buffy crew wasn’t exempt from the jovial vibe of the shooting, either. Noxon gets her own mini showcase, appearing briefly as a woman charged with a parking ticket, dramatically pleading with an officer during a conversation between Buffy, Xander, and Giles. On top of that, when the Scoobies first convene to talk about their sudden bursts of song, they wonder whether anyone else in Sunnydale has been affected. As Buffy opens the door to the bookstore, Fury gets a brief but extremely memorable cameo, holding a dry-cleaned shirt and belting, “They got the mustard out!” alongside a group of backup singers, which included Noxon and Shankman, and two stuntmen doing front flips. “It’s not just us,” Buffy deadpans.

Getting the show’s longtime producers and crew involved added to the feeling on set that the episode was something special — a wacky tribute to the people who had made Buffy what it was. But not all the producers wanted their moment in the spotlight. “That’s not my thing,” Solomon said. “I stay low and out of the way and behind the scenes. But we were thrilled to have the other guys do it, and they were funny as hell.”

“Once More, With Feeling” holds a fascinating place in the Buffy canon. It is the best episode of the series, though it’s smack dab in the middle of the show’s most controversial and derided season. Season 6 isn’t reflected on nearly as fondly as other Buffy years; Season 5 could have been an exemplary coda for the show after Buffy’s world-saving sacrifice, and her resurrection in Season 6 felt like an unnecessary development more worthy of a soap opera — to say nothing of Willow’s villainous turn and Spike’s late-season attempted rape.

But “Once More, With Feeling” transcends these criticisms. What gives the episode its resonance isn’t just the music, but the crucial narrative developments that would stick to Buffy’s characters through the end of the show’s run. When a series airs a musical episode, the premise usually comes with a catch: In Grey’s Anatomy, the musical episode was downplayed as a hallucination. A more recent The Flash–Supergirl crossover episode saw its characters thrown into an alternate universe at the whim of a villain called the Music Meister — naturally, they were forced to escape this predicament via song. Often, the musical gimmick is thrown out to deliver some much-needed hype for a show bleeding viewers late in its run. Seven seasons and 110 episodes into its eight-year run, the USA Network drama Psych went for a musical of its own. (Perhaps, by Season 14, The Walking Dead will give it a shot.)

Not only did Buffy avoid those pitfalls, but it subverted what fans expect from the concept. Laid bare, the narrative progress from “Once More, With Feeling” more than justifies the musical’s existence. “So many of the characters were going through so many serious things, and then it was set to music, which gives it a light touch, but it’s sort of a delivery system,” Solomon said. “It makes it very palatable, so you’re enjoying listening to the music and hearing the funny things, and then suddenly you feel like crying because it’s heartbreaking.”

While the anti–Season 6 camp’s concerns shouldn’t be dismissed, the season also deserves praise for its ambition. A show that often used its monsters as metaphors to convey the social problems that adolescents go through now had characters frequently confronting their own demons — an uncomfortable and compelling watch by design. The apex of the season, however, is the musical: an exhilarating package that served as a bridge between Whedon’s signature witticisms and the brooding undertones that late-era Buffy perhaps necessitated. “Once More, With Feeling” was the 107th (!) episode of Buffy the Vampire Slayer, which would hit 144 episodes by the end of the seventh and final season. That the series continually managed to conjure up imaginative monsters of the week, ominous season-long villains, and ruminative explorations on personhood was impressive in its own right; churning out a musical that’s fun, catchy, and, most of all, important to the plot past its centennial mark is miraculous. “Honestly, it was a magical time,” Solomon said. “I hate to say it, it sounds so ridiculous, but it was.”