The only bad thing about the abundance of intriguing and entertaining characters in Buffy the Vampire Slayer is that sometimes, the story can't do all of them justice.
- Whistler, the mysterious and enormously popular agent of the Powers That Be, who was originally supposed to be Doyle on Angel, but the actor was busy with other projects and they created the character of Doyle instead.
- In "Out Of Mind, Out Of Sight", an episode was about a student Marcie Ross who can turn invisible and by the end of this episode was taken by F.B.I agents to be trained in assassination and espionage. She never appeared again. Then again, it's debatable to see whether she "appeared" at all.
- Kendra, the secondary Slayer introduced in Season 2 who was called after Buffy's temporary death in Season 1. Very little of her character and background was explored before she was killed off towards the end of the second season. Given the show's habit of sparing characters originally intended to die once they realised their potential (Jenny, Oz, Spike, Faith) it begs the question how no one could have seen Kendra's - especially since her death in "Becoming" could have easily been rewritten to just have her taken prisoner without changing the story too much.
- Dracula. A famous vampire with mysterious powersnote , has history with both Spike and Anya and is able to really get under Buffy's skin. His single episode ends with him being mocked and leaving, most of the episode really more focused on foreshadowing things about the main characters. The comics at least make more use of him, in particular his weird relationship with his friend/meat puppet Xander.
- Professor Maggie Walsh was shaping up to be an interesting arc villain in Season 4 - a human Well-Intentioned Extremist who shared many of Buffy's goals, had personal relationships with Buffy, Willow and Riley, and at one point even eclipsed Giles as a mentor figure for Buffy. Alas, she was killed halfway through the season and replaced by her own creation, the far less relatable human-demon-cyborg hybrid Adam, who barely interacted with the main cast.
- Adam himself could have been an even more interesting antagonist, perhaps exploring his genesis and the morality of the organization that made him, which might have lead to a Heel–Face Turn or at least him becoming an Anti-Villain who developed his own goals and motivations who might even end up turning on his masters. Instead, he remained a shallow one-note villian until his demise in the finale. It didn't help that he was introduced very late in the season.
- The original plan for Sunday, the vampire Buffy faces in the first episode of Season 4, was that she was a previous slayer turned vampire. Seeds of this storyline remain in the episode, particularly in Sunday’s uncanny savviness against Buffy. One has to wonder why that idea wasn’t resurrected when Walsh had to be written out, rather than the introduction of pretty universally disliked Frankenstein Expy Adam.
- Dawn is an inter-dimensional key to hell dimensions in human form but was given no powers, and is largely used as a helpless Damsel in Distress for most of her time on the show. The comics take better advantage of Dawn's origins, granting her portal-opening powers in Season 10, but even then, it was used rather scarcely.
- Amy Madison feels like she could have been a more regular character after being restored to her human body, and maybe even a member of the gang with some nice new personality traits that positively develop her friendship with Willow instead of only having a few more (somewhat antagonistic) appearances. The All There in the Manual yearbook implies that she can think as a rat and communicate with her friends through writing, while appreciating how they are taking care of her, but this interesting aspect of her character never makes an appearance in the show itself.
- Vampire barfly Sandy has a bit of flirtation with Riley and seems like a rare non-murderous vampire. The fact that she was turned by Vampire Willow also gives her an interesting connection to the main cast, but she's killed off in her third appearance without doing anything of note beyond kick-starting Riley's vampire bite addiction arc.
- Principal Robin Wood was a great addition to the cast in Season 7, an easy-going principal who's the son of the Slayer that Spike killed in New York in 1977. Following the resolution to their feud, he fades into the background in the last few episodes, as if the show didn't know what to do with him beyond that arc, beside having him hook up with Faith. In fact, the reason his fate is ambiguous in the finale is because Joss Whedon literally couldn't decide whether to kill him off or not.
- Many of the surviving Sunnydale High one-shot students such as Chris Epps (a Reluctant Mad Scientist and friend of Willow), Eric Gittleson (Chris’s less reluctant fellow Mad Scientist), The Pack (whose reactions to coming to grips with their actions as cannibalistic werehyenas are only covered in All There in the Manual sources), Buffy’s first boyfriend Owen (an aspiring Warrior Poet), Homecoming Queen candidates Holly and Michelle, Michael (the only boy in the magic group Willow is part of), Friend to Bugs Wendell Sears, and Xander’s car-obsessed Romantic False Lead Lysette can feel underused. It would have been interesting to see such characters recur, have different views of the main cast, and maybe get scenes and lines during "The Wish" and/or "Graduation", but none of them appear in any episodes besides their debuts.
- Potential Slayer Amanda is viewed as one of the only potentials with an entertaining personality and skill set that is evident even when she spends many of her appearances just being a Spear Carrier with a rounded personality. She has enough geeky interests to play D&D with Xander and Andrew and is a Sunnydale native who has known Buffy and Dawn for some time and has some good Action Girl accomplishments. All of this gave her the potential to be developed a lot in post-Season 7 media, where it would be easier to broaden the character focus beyond the main cast. Instead, she is apparently killed in the Season 7 finale to provide a little extra Collateral Angst and is never mentioned again.
- Potential Slayer Chao-Ahn could have been one of the best Potentials if her arc of being a Naïve Newcomer who never had a Watcher and is ignorant about the supernatural while being mentored by people who are separated from her by a Language Barrier hadn't been played entirely for laughs and either season 7 or the sequel comics (the latter of which she is absent from, she does have a notable role in the 2020 novel Chosen) had given her some dramatic moments in dealing with learning about the supernatural, working with the other Slayers, and maybe showcasing more of her Chinese cultural background.
- Molly links up with the heroes at the same time as Kennedy and could have been used as a decent Foil to her due to their shared introduction, different class backgrounds, Molly being the nicer of the pair, and Molly killing a vampire before any of the other Potentials. However, she is absent from several episodes between her first and last appearances, only plays minor roles in several of her episodes, and loses some gravitas due to her Fake Brit actress having to give her a highly noticeable bad accent.
- Sunnydale guidance counselor Mr. Platt is an understanding authority figure who gives Buffy advice that applies to her school life and work as the Slayer. Fans would have loved him to become a mainstay for the rest of the season or longer, especially given the number of upcoming situations Buffy could have used a therapist to talk to about. Instead, he's murdered before ever getting another chance to talk to Buffy.
- The German Perky Goth Potential Slayer from "Beneath You" is a short-lived Pursued Protagonist, but her colorful wardrobe and the chase she puts up make some fans think that she had the potential to be a better recurring character than most of the Potential Slayers who survive to become Mauve Shirts. Her death wasn't even necessary to demonstrate the threat of the new villains, as they had already been shown chasing and killing a different Red Shirt Potential in the previous episode.
- Buffy's Hemrey High Girl Posse only appears in one short flashback scene to right before she is chosen as a Slayer and aren't even portrayed very similarly to their counterparts from the original movie. Some fans would have liked seeing at least one of them show up again to take in all of the ways Buffy has both changed and stayed the same since coming to Sunnydale. Assuming they are the same characters from the film, it would have also been nice to explore the aftermath of one of them killing a vampire during the prom battle and another dating Buffy's old boyfriend but then regretting it.
- The Expanded Universe novels have many original characters who feel like they could have recurred and/or appeared more in their sole book.
- Revenant features an Occult Detective named Art Sledge who rescues the heroes from danger, comes across as a Hero of Another Story, and then proceeds to sit out the rest of the book’s action on the sidelines and never shows up again.
- Trevor Kensington from Spike & Dru: Pretty Maids All in a Row is an ancient Watchers Council director who knows some powerful magical spells, is one of the more humble and insightful leaders of the organization, and has some apparent It's Personal history with the Big Bad. He never gets any conversations with the Potential Slayers and falls after a quick battle with the Big Bad (although he does kill several Mooks) without any details of their past encounters being given.
- Resurrective Immortality-enjoying Veronique from Immortal, apparent Daywalking Vampire Solitaire from Ghoul Trouble, Benevolent Boss vampire fairy and sworn enemy of Anya Queen Mab from Little Things, vampirized ex-Slayer Celina from Tempted Champions, time-traveling vampire wizard Lucien from Portal Through Time, and A.I. Is a Crapshoot Mysterious Informant Simon from Mortal Fear are all unique and interesting major villains whose existence or status adds a lot to the supernatural status quo, but none of them appear in more than one book.
- Callie, the Tragic Villain Undead Child who hates Angelus but adores Spike in One Thing or Your Mother is burned by the sun long before getting a chance to have her worldview complicated by seeing Angel or Spike in their ensouled states.
- The fishing boat crew members (including an undercover cop who one of her coworkers has a crush on) and high school students captured by the Flying Dutchmen in Ghost Roads all get interesting introductions that feel like they could have had decent roles throughout the book or beyond. However, they are all either quickly killed after choosing death in a Join or Die scenario or never get a chance to interact with Giles while they are all prisoners together and he is plotting to escape.
- In Return to Chaos, Amanda Singer has disappointingly few interactions with her Hunter of Monsters Druid cousins after introducing them to Buffy while seeking to remain an Agent Scully.
- None of the Ragtag Bunch of Misfits recruited into a witch coven in Prime Evil get too much focus on developing their Odd Friendships or realizing Buffy is right about their leader in the climax, and some never even reveal their reasons for needing magical powers.
- Rosanna Jergens from The Wisdom of War works for a group trying to form treaties with supernatural races rather than fight them like the Watchers, is willing to be a Cowboy Cop against truly dangerous creatures, and has good chemistry with Giles, but her book ends with her on bad terms with the Scoobies and never contacting them again.
- The past Slayers from the Tales of the Slayer short stories mostly work well as the protagonists of self-contained short stories, but it can be disappointing that Beatnik Zoe Kuryakin from "Undeadsville" (who manages to keep her soul after becoming a vampire but chooses to commit Suicide by Sunlight rather than work to be a Friendly Neighborhood Vampire), Pirate Girl Robin Whitby, Thessily Thessaloniki (who lasts longer than any other known Slayer before the 21st century), Asha Sayre (a black Slayer who dies too early in her war with vampire members of The Klan), and carnie Slayer Millie Rose Gresham have so little of their adventures shown.
- In the Tales of the Slayer novella "Ch'ing Shih", most of the orphaned girls Xiaoquin has been protecting are Red Shirts when they could have been her version of the Scooby Gang.
