Everyone knows Kal Penn from Harold and Kumar, but only a few his single appearance as a minor character in Buffy the Vampire Slayer. Buffy is a world rich with minor characters, and plenty of them recur in unexpected ways, like Clem (James C. Leary), or become major characters, like Spike (James Marsters).
But some of those with bit parts went on to become Hollywood powerhouses, like Kal Penn, who played a caveman college student in "Beer Bad" (Season 4 Episode 5), or Amy Adams, who guest-starred as Tara's sister, Beth Mclay, in "Family" (Season 6 Episode 5). But, still, only a few guest stars manage to stand out in just one appearance alone.
Sweet (“Once More With Feeling” Season 6 Episode 7)
Easily the coolest demon to ever appear on Buffy, Sweet (Hinton Battle) strolls into Sunnydale with tap numbers so fire the dancers burst into flames. In a single episode-- the best of the series, according to IMDb-- he gives us a full album of wall-to-wall unforgettable hits, then disappears unscathed.
Sweet is ed not only for his talents in song and dance but also for his smooth attitude. Even when a wrench is thrown in his plans, he stays calm and collected. It's rare for a demon written by Joss Whedon to be so human without being goofy and nonthreatening, and the demons that the scooby gang faces are often more animalistic or robotic. Not to mention Sweet's solo is one of the best songs of the bunch. From his bright-colored suits to his pipes of gold, Sweet is incredibly memorable.
Marcie (“Out Of Mind… Out Of Sight” Season 1 Episode 11)
Marcie is one of the more sympathetic villains of Buffy’s first season. Portrayed by Clea Duvall, who would go on to star in Girl, Interrupted and But I’m a Cheerleader, Marcie is a neglected girl that turns into a violent invisible threat.
Her campy prom aesthetics, wit, and misunderstood attitude make her a prototypical Enid (Ghost World). Like Enid, Marcie is relatable to a lot of young girls that don't fit in. Not only are they both cynical and arcane, but they also both disappear-- Enid on a bus ride, and Marcie very literally. The FBI eventually takes over Marcie’s capture, the show’s first indication that the government is aware of supernatural activity. This would come into play in the later seasons with Riley and the Initiative.
April (“I Was Made To Love You” Season 5 Episode 15)
April, played by Shonda Farr, is the robot through which Buffy is introduced to one of the major players of the sixth season, Warren (Adam Bush).
Built to be the perfect companion, April is lovable, sweet, and comionate. Her final scene with Buffy, wherein she grapples with existential questions and is left to wait until her “death” for a man that would never come, is nothing short of heartbreaking. April is a prototype for the Buffybot, a recurring character of the later seasons that serves as an ugly manifestation of Spike’s creepy desires in the same way that April does for Warren.
Jack O’Toole (“The Zeppo” Season 3 Episode 13)
Jack O’Toole, played by Channon Roe, is the school bad boy that bullies Xander (Nicholas Brendon) into a night of raising hell with several of his undead buddies.
The immaturity and recklessness of Jack and his friends lead them to wield their power erratically, but it also allows for Xander to prove himself as a hero. Jack is a comedic villain that meets his match in Xander, a comedic character. More to the point, Jack and his friends are hilariously dumb, rising from the grave to say things like "dude." It’s amusing to see how such an idiotic guy wields supernatural power, especially when it's up against Xander's humanity and wit.
Dracula (“Buffy Vs. Dracula” Season 5 Episode 1)
It was only a matter of time before the Slayer faced the most iconic vampire of all time-- Dracula (Rudolf Martin). For much of his episode, he holds Buffy under an inexplicable spell that leads her to allow him to bite her and even go as far as to drink his blood as well.
Dracula turns out to be kind of weird, and strikingly similar to Angel-- brooding, a fan of late-night visits, and looking for a slow-burning, ionate kill. When Buffy insists that “last night will never happen again,” Dracula takes on the role of a manipulative boyfriend, daring her to stop him. He’s the world’s most famous vampire for a reason, and his allure is undeniable. It makes sense that he has a special power over Buffy, whose dating history would suggest she is drawn to vampires.
Olaf (“The Triangle” Season 5 Episode 11)
Olaf (Abraham Benrubi) is a troll that is accidentally summoned by Anya and Willow into modern-day Sunnydale. Upon arriving, he reveals himself to be Anya’s ex-boyfriend and her first victim as a vengeance demon.
Though he technically does also appear in flashbacks in “Selfless” (Season 5 Episode 7), he manages to make a huge impression in one episode alone and plays a huge part in Anya's backstory. Olaf loves beer, causing fights and ex-girlfriend drama, which would make him a great reality show contestant. He may not be likable, but he sure is entertaining.
She-mantis “Natalie French” (“Teacher’s Pet” Season 1 Episode 4)
The predatory She-mantis (Musetta Vander), who goes by the alias Natalie French, poses as the new substitute science teacher at Sunnydale High.
Although she only appears in one episode-- Jersey Shore) of Buffy, She-mantis is mentioned at least six more times and alluded to several more, establishing Xander’s reputation for attracting demonic women. The mantis’ methods may be brutal, but the violent sexuality of the female is fascinating, emasculating and comes to define Xander as a man. She’s a little one-note, but the femme fatale trope is still fun to watch play out.
Lissa (Season 7 Episode 4)
Lissa, a girl Xander hopes to date in a rebound from his relationship with Anya, is notably portrayed by recording artist Ashanti. Even though she has no idea about his connections to the Slayer, Lissa ties Xander to a pentagram and tries to use him as a sacrifice.
Lissa is powerful, has playful banter, and she moves the story along as a direct connection to The First, the biggest Buffy villain ever. It's fun to see a musical artist flex their acting muscle in a bit part, and at the time Ashanti was topping the charts. She also recalls the show’s running joke of Xander being a magnet for demon women for one final time, which earns her a spot among the top one-episode characters.
Billy “Ford” Fordham (“Lie To Me” Season 2 Episode 7)
Billy Fordham, known affectionately to Buffy as Ford (Jason Behr), is an old crush of Buffy’s that moves to town. His big secret is that he and a group of other teenagers plan to get turned into vampires.
Essentially, Ford is a huge idiot, which makes him very fun to watch. The vampire craze would only accelerate in the next decade with the release of Twilight, making Ford and his friends a prolific and hilarious critique of a cultural phenomenon that would only become more popular in years to come. Although Ford reveals himself to be a total loser, his betrayal is a huge emotional blow for Buffy, which gives Ford a little extra significance.