The character is brilliant. They might be any role but no matter what trope they fall under, whether a single trope or many, they all have one thing in common. You love them, but the writer doesn't. It's not their fault, they do the best they can. They just never seem to get the screentime that you think they deserve. That Day in the Limelight isn't forthcoming, the episode focusing on their mysterious past doesn't turn up, you never get to hear their snarky remarks on a situation that just calls for it and after five pages of teasing they get Put on a Bus to Nowhereville.
Often happens when a single- or few-episode character is introduced. They show great promise, with an interesting background or interaction with the main character(s), and could have led to a compelling plot or new dynamic if made a permanent fixture, or at least a recurring character — but were underdeveloped and then discarded. Occasionally this happens to someone whose backstory is revealed in supplementary materials, or in a video game are filled through sidequests, which are very likely to be skipped and ignored, although it's especially annoying if these supplementary materials were never available in your country.
Contrast Creator's Pet, this trope's exact opposite, where a character isn't considered good by many viewers but keeps getting exposure anyway. A subtrope of They Wasted a Perfectly Good Plot, supertrope of Too Cool to Live. Nearly always an Ensemble Dark Horse. Fan Fic writers are especially drawn to these characters, as the Fanfic Fuel they generate can be prompts for many stories.
Raditz is Goku's older brother, but after his defeat and death, he's rarely if ever brought up ever again. Dragon Ball Z Abridged lampoons this, with Krillin asking Raditz "You'll be involved in many future events, right?", to which Raditz responds by an annoyed silence before attacking Krillin.
There's a substantial minority of Dragon Ball fans who feel this way about pretty much any martial artist who isn't at least half Saiyan. Despite their interesting personalities and techniques, the human and Namekian characters rarely get to do much besides fall victim to The Worf Effect, serve as the Butt Monkey, or otherwise just act as glorified benchwarmers who Can't Catch Up.
The Jinchuuriki, since all of them except Naruto, Killer Bee and Gaara were killed and captured off-screen. However, Utakata was given his own filler arc in the anime.
Some fans feel this way about various Akatsuki members who were killed off, at least before those who were resurrected by Kabuto's Edo Tensei spell returned. Notable examples include Hidan and Kakuzu.
Hanabi Hyuuga. We haven't seen her in nearly 500 chapters. She is mentioned in passing implying that she has at least become a Genin by the Pain Invasion Arc, which is impressive since she's 10-11, whereas the quite proficient Teams 7, 8 and 10 were all 12 by the time they made Genin. Another question is how she fits into the Hyuuga line of succession- Hiashi says in a flashback around the time Hinata became a Genin that Hinata is worth less than Hanabi is, although since Hinata Took a Level in Badass, this may no longer be true. However, some fans, especially fanfic authors, suggest that Hinata has been or will be passed over as head of the clan in favor of Hanabi.
Another prime example is Anko Mitarashi. Despite her connection to one of the main villains and consequently to the plot, she remains almost completely out of focus, and serves only the sad function of a plot device. She hasn't even been seen or mentioned since said kidnapping leaving many to wonder her fate.
While we're speaking of characters related to one of the main villains, Yamato is left Out of Focus way too much for someone who was with Team 7. He basically ends up existing to control the Kyuubi, and then to get kidnapped as soon as Naruto learns to control his transformations.
Kabuto is also this to some, after revealing his mastery of Edo Tensei, obtaining Sage Mode and creating an army from some of the greatest ninjas ever he looked to be in a prime position be a potential Big Bad and his background made you feel for the guy. But he gets worfed by Itachi easily and all he's done is reversed, like Anko he hasn't been seen ever since what he did was reversed, which irritates some as a Medic who was revealed to be friends with him growing up at the orphanage was shown during the war wondering if he was still alive.
Yuugao Uzuki was introduced as Hayate's fiance and one of the people to find his body. Her likely grudge against Suna in general and Baki in particular never comes up.
RockLee, though arguably this isn't so bad if you count the fillers in Part I & II.
An interesting case is Shino Aburame, who is one of the more prominently featured of the Konoha 12 and clearly built up as one of the biggest players of the Chuunin Exams, on par with the likes of Shikamaru, his prominence abruptly dropped off with his exclusion from the Sasuke Retrieval Arc, and he's been mostly Out of Focus ever since.
Many of the Arrancars were unexpectedly popular with readers, both domestic and abroad, so Kubo was pushed by his editors to give the Arrancar A Day in the Limelight to please the fans. Unfortunately, this meant many of the Arrancars, as well as other characters during this conflict, were either shafted or killed much earlier than people wanted.
Rudbornn Chelute, the head of the Exequias, is the only Arrancar with a fully intact mask. The point of being an Arrancar is that they have broken masks, so he's quite the enigma. He's the leader of the Exequias, a group of Faceless Goons who have the same type of skull; they're spawned by Rudbornn himself, making him a non-video game version of a Mook Maker. He apparently kills off a few minor antagonists once they've outlived their usefulness and sort of disappears for a little while. Toward the end of the Hueco Mundo arc, he has a brief fight with Rukia in the manga, a full-episode fight against Rukia, Renji, and Chad in the anime... until he's smashed to pieces by Yammy before we find out anything really significant about him. There's a chance he's still alive in the manga, but we've yet to see him since.
The Privarons are former Espadas who were demoted in favor of the newer, more "enhanced" ones that everyone knows about now. They consisted of Dordoni Alessandro del Socaccio, Cirucci Sanderwicci and Gantenbainne Mosqueda, each with their own distinct designs, abilities and personalities, with Dordoni and especially Cirucci being the ones that fans latched onto. Gantenbainne, while alive, has been MIA for an ungodly amount of time, while the other two were seemingly killed by Rudbornn and experimented by Szayelaporro. It's implied that their bodies were the ones found by Mayuri in Szayelaporro's lab after the latter was killed, and Kubo has said that the bodies will be important to the final arc. We've even seen such a body laying down on a table in front of Mayuri and Nemu, so there's a chance we'll finally see what's happened to them.
The Fullbringers from Xcution. A lot of fans felt that their arc was little more than filler, meant to restore Ichigo's powers, although most got a backstory and even some Character Development before they left the map. Though now that at least three of them have returned and are likely to be on the hero's side for the final conflict, this may not hold true forever.
Kon's introductory arc paints him as a considerably more serious character, refusing to take life as a result of having lived in fear of being discarded. After this, though, he's mostly portrayed as perverted comic relief and occupies Ichigo's body whenever he goes out as a Soul Reaper.
Tatsuki Arisawa. She's a childhood friend of Ichigo and Orihime's best friend. She and Ichigo had a friendly rivalry when they were kids as karate partners (in which she would always beat him), and helped him cope with his mother's death. She was also involved in several incidents early in the story, and circumstances made it seem like she was going to develop powers at the same time Chad and Orihime did. Then...nothing. She ended up Locked Out of the Loop, knowing that her two closest friends were involved in something, but was kept in the dark for the next 3 story arcs. It gets to the point where the viewer is as frustrated about her role as she is, although there's a growing appreciation in her representing the parts of the living world Ichigo is leaving behind. Word of God is that this wasn't supposed to be the case; he was planning on developing Tatsuki further, but had to back out because Shueisha wanted him to hurry up with introducing the Shinigami.
Retsu Unohana ended up being one of the most extreme cases. Despite being calm and almost always having a smile on her face, she scared the living shit out of the other characters. Background books listed her as being the third strongest captain. Despite all that, for most of the series she was on the sidelines, only stepping in when someone needed healing. It's finally revealed that she was actually the worst criminal Soul Society had ever seen, and was responsible for Kenpachi's love of fighting. To counter the villains, Unohana trains Zaraki to unlock his full power, with the cost being that he'll kill her once he's reached that stage. She dies happy that she could help bring him to his full potential. Complaints about this turn of events are many—from people who feel that her revealed characterization made it seem like the motherly healer was a disguise instead of an attempt at redemption, that it was an incredibly stupid decision in-story, and that it felt like a shining example of sexism in Shonen manga. The end result is that a character fans had waited a decade to see in action dies solely to empower a character fans were beginning to feel was already too powerful.
The House of Kyoto, the heads of the major industries in Japan, who later assist the Black Knights by supplying them with technology after one of them, Kirihara, recognizes Zero as Lelouch who he met as a child. It would've been nice if all the members and not just Kaguya were elaborated in character or if Kirhara's past relationship with Lelouch was explored more, rather than executing them off-screen between seasons for being the Black Knights' supporters.
After R2, the list could include: Ohgi, Diethard, Toudou and the Four Holy Swords, Tamaki or even V.V.
Shirley and Euphemia at least had more development than the others before dying, but even more could have been done by keeping them alive. In fact, the producers seem to agree; several AU spin-offs end up keeping one or both of these characters alive.
Several of the Knights Of Round, who could've been an elite Quirky Mini Boss Squad, but most of them ultimately became cannon fodder to show how skilled Suzaku and Kallen are.
Naomi Misora. Competent FBI agent. Developed and multidimensional. Has a very good reason and more than enough skill to bring Kira down. Dies less than three episodes after being introduced, crushed by a massive Idiot Ball. According to Word of God, she was meant to last a while longer and have a lasting impact on the plot, but she was far too clever and would have figured Light out before long (particularly, she had already pieced together that Kira can kill by means other than just heart attack, something that it was way too soon for L to know about), bringing the story to a quick end. Perhaps in compensation, the live action movie sees her role expanded from the manga, although she still does die.
Matt. There is a reason why he is the Ensemble Darkhorse despite only having four lines before he becomes roadkill. Not only does he have a cool character design is he L's third prodigy and he and Mello's close but ambiguous relationship is the closest there is to variety amongst the relationships of its genius characters when all others (L and Light, L and B, Near and Mello, Light and Near, Light and Mello and persumably L and the other detectives) are very similar with them all having admiration/respect for the other but ultimately being unable to work with them and being rivals.
Mobile Suit Gundam 00: Nena Trinity. She's introduced, like her brothers, as an unsettling figure and later crosses the Moral Event Horizon by killing all of Louise's family. Then Ali Al-Saachez unknowingly gives her a taste of her own medicine by killing her brothers and leaving her all alone. Now in season 2, this seems to have affected her and she's slightly less batshit insane and more thoughtful. She also has to work with an even bigger spoiled, sociopathic villainess, giving her someone to reflect on. She later helps out the cause of good, not due to a Heel-Face Turn, but because her side isn't living up to her standards. All the while, Louise is becoming a Dark Action Girl and out for revenge against Nena. This would be a great plot: have Louise face Nena now that Nena has somewhat redeemed herself and is beginning to change for the better. It would be a fascinating conflict of Grey and Gray Morality. So what happens? A Time Skip occurs, Nena is suddenly as much of a psychotic bitch as before, she discards her standards, and, though she does awesomely get rid of Wang Lui Mei, nothing really happens to even out the conflict between her and Louise. Which leaves the question: What was the POINT of trying to develop Nena's character if the staff was just going to end her THIS way?!
Titus/Thetis, perhaps the only MotW to show something like human emotion, and hints of a backstory connecting her with Jedite (Jadeite). None of this ever gets developed, as she's only in one episode. And Jedite himself, who also got some hints of character in that episode, is done away with in the very next one.
Two particular Monsters of the Week qualify for killing major characters. Zoycite/Zoisite's Negamonster Housenka stabs Neflite/Nephrite to death, and Mr. Magic Pierrot, the Lemures who serves Para Para, kills Hawk's Eye and indirectly causes the deaths of Tiger's Eye and Fish Eye as well (although unlike Neflite, the trio are revived). Like Thetis, both MotWs are killed in their first and only episode.
Rui Saionji, Molly/Naru's "sister", had potential in her own right and could have been used to develop Naru's character and history. Also only appears in one episode.
Sam/Shingo's girlfriend Mika and Ami's boyfriend Ryou get two episodes each. Makoto's best friend Shinozaki gets only one.
Although she has a much bigger role than the above examples, Molly herself qualifies. After two seasons of being just Serena/Usagi's "normal" friend, it seems for a moment she's going to discover (or reveal that she knows) the truth about the Sailor Scouts and so transition into a new role. Instead, from this moment on she disappears from the plot almost completely.
Pretty much all of Sailor Galaxia's minions qualify as wasted, especially compared to past Quirky Miniboss Squad members. Also, three out of five of the Witches 5 from Sailor Moon S, who only got one episode each to themselves whereas the first two had at least around fifteen each.
Motoki qualifies - he runs the arcade the Senshi spend much of their free time at, is pretty much the only friend Mamoru seems to have, both his sister and his girlfriend are targeted by the bad guys (twice for both of them), and yet somehow, he himself is never targeting, seeming to just hang around in the background. In the manga, he learned the identities of the Sailor Senshi, but in the anime, he didn't even get that.
Lyrical Nanoha has Yuuno Scrya. In a series so focused on how the ancient civilizations and technologies of the past are constantly unearthing themselves to cause major trouble in the present day, having an archeologist, scholar and librarian of ancient knowledge in the cast was a great idea. But despite his many virtues and all of the potential left to explore with his background and career, the writers seemed to only care about him as a romantic possibility for the eponymous heroine. So when they decided not to do that any more, they took him completely out of the action and plot without a word of explanation, even when the rest of the cast should have been still looking to rely on his support in battle (while in terms of offense he's mediocre at best, his defense is almost perfect, he's the only person in the entire history of the franchise who can forcibly teleport an unwilling target, and he doesn't even have a device to help himnote Given how magic functions in the Nanoha-verse, that means he's doing very complex mathematical equations completely in his head, while other mages are attacking him.), or at least asking him what the heck they're dealing with this time. Yuuno even teaches magic to Nanoha's adoptive daughter, Vivio, according tothe side-materials, but we never actually see or hear them interact, even when she visits his library to do what was originally his role in the story.
Ash's Primeape, which he caught in one episode, didn't use until a few episodes later, at the end of which he gave it away, and it hasn't been heard from since.
Ash's Glalie hadn't really been used after he left it at Prof. Oak's ranch, even if its main purpose was more than likely to help Ash in the Hoenn League. Ash's Torterra is another egregious example. When it was a Turtwig, it did rather well, winning Ash his first badge and helping out in other major battles. As soon as Ash got Chimchar, however, Turtwig may as well not have even been around. When it became a Torterra, it became subject to The Worf Effect, and never got any notable wins.
The very first appearance of Teams Magma/Aqua and the last are less than 100 episodes apart. So how much screen time did the Teams get? Only 6 for Magma (not counting a two-shot member with a Ditto, who served no major role at all), and 7 for Aqua - and out of these, their leaders only appeared in the two-parter which ended their arc, with very little character development as the writers chose to focus - again - on Ash and Pikachu as opposed to developing the conflict better. And most of these episodes had both teams so there's even less development. Given how they were loads more competent as adversaries and have interesting motivations, scrapping the opportunity to use them feels like a complete waste.
Team Galactic fares a little better, but still only get 10 episodes out of well over 100.
Team Rocket themselves haven't prominently appeared since the Kanto saga, and even then we were mostly limited to the bumbling trio. This looks to be subverted - mercifully - with greater plot and story development in the Best Wishes series, however.
Steven Stone, Hoenn League Champion in Ruby and Sapphire, and most powerful NPC in Emerald, was reduced to a Character of the Day in his one Hoenn appearance. Even worse, said portrayal of him was shown to be hypocritical, berating Team Rocket for digging a hole in the cave while he sends them flying through the cave roof with his Aggron. Oddly enough, his role in the Team Aqua/Magma plot is filled in by Lance.
Ogawa of Bakuman。. He's incredibly knowledgeable about manga, from his prediction that Detective Trap wouldn't last long in Jump to knowing how to set up an office and manage assistants. Despite his talent, he doesn't try to become an mangaka, not even trying to pair up with a writer to offset his weaknesses as a storyteller, and is never seen again after Trap gets canceled. He does make a return as one of Ashirogi Muto's assistants once they start on Reversi.
Black Butler: Despite an impressive cast, most characters who aren't Sebastian or Ciel become dead weight pretty quickly. Not to say that many aren't Flat, but many others showed serious promise before being unceremoniously killed or forgotten. It's especially problematic when two such characters are the season's Big Bads.
Digimon Adventure 02 had numerous examples of wasted plots, but two infamous ones were the aborted Dagomon arc and later the Demon Corps. Both characters could also count as wasted.
Since Digimon Frontier had already went past the point dropping the concept of Mons in favor of a Henshin Hero gimmick, the least they could've done was have the four children (Katsuhito, Teppei, Teruo, Chiaki) who show up in the Digital World as four additional sixth rangers who would be given the four recently defeated legendary warriors in their possession. However, the main cast tell them to just go home, claiming that the Digital World isn't safe.
This can also apply to ANY Digimon (without a default level) that has debuted in Digimon Xros Wars, considering how they could've fit into and complete any digivolution line that certain fans would consider a complete mess.
Yurin L'Ciel is established to be an X-Rounder, this series' equivalent of a Newtype. She's conscripted by the Unknown Enemy for this ability. So of course you immediately hand her over to a seven-year-old psychotic brat who's already proven himself too capricious to be a commander and who gets her killed in the first battle she's used in by his carelessness. Why? To motivate Flit, because just killing his mom and exclusively targeting civilian colonies isn't enough to make him hate the Unknown Enemy forever. But mostly, it's because in a Gundam show, the Newtype girlfriend dies, and by gum the whole franchise will end if we break that rule.
In the third generation, Clanche pilot Shanalua Mullen coaches Kio in how to be a better pilot, pulling him away from the dangerous habits he developed from his simulations and reminding him that even enemy pilots have families, so he should not be so gleeful about defeating them, and generally being a Cool Big Sis. It turns out she's The Mole so she can pay for her sister's hospitalization and she dies in a Heroic Sacrifice shortly after being found out. Which is maybe four episodes into Kio's arc. But don't worry, Derek and Jonothan are okay! You know, those two guys who barely even meet the significance requirement to be Those Two Guys.
Only a select few of the many Angel Beats! characters were expanded on. This leaves fans wondering about the many gag characters and one-offs. Even with some of the characters that were expanded on, like Hinata or even Yuri, we never learn how they died or much of their backstory. This is the fault of Executive Meddling. The anime was originally going to be 26 episodes long, but was suddenly cut down to 13, leaving little time to properly focus on these characters.
Planet Robo Danguard Ace: Captain Dan/Ichimonji Dantetsu is the best pilot in the whole series, drop dead gorgeous, tormented beyond the dreams of even the most ardent Condor Joe wannabe, with a deep, tragic and heart-rending backstory (mind-controlled, forced to kill his fellow test pilots, mind-wiped and tortured/enslaved for 10 years, missing out on his son's growing up, forced to hide the return of his memories and enduring several potentially career-ending injuries). To top THAT he's a determinator and all round bad-ass who could put Captain Harlock to shame - none of which is fully realised given the times and the demographic.
Queen Millennia: The TV series gives us the Man in the Trenchcoat. No name, no backstory, but this guy is so cool HE WEARS SUNGLASSES TO PILOT A SPACESHIP. Obviously has a great deal of history with the other wasted opportunity, Selene - and frankly both of them are way more interesting than the eponymous heroine and her pint sized sidekick.
In the non-Macekre'd version of the series, Selene is a very important person and her motivations are explained.
Ozuma: back to amnesiac men in masks again. Several viewers were more interested in the horrific implications of Dick/Guido's backstory than in the rather lame ecological message.
The Galaxy Railways: Wattaru Yuuki. It's possible the entire pre-series crew of Sirius Squad are way more interesting than the cast we got, but the brief glimpses we get of Captain Yuuki (all-round good-egg, wonderful father, caring husband, heroic role-model...) leave the viewer begging for more. He's used to COMPLETELY deconstruct Harlock's lone-man heroics but given so little screen time to do it in you have to be a major Matsumoto buff to catch it - if you do, you'll need an entire box of kleenex by the end of season 2.
Smile Pretty Cure! has Miyuki's grandmother, a woman who proves that she has Kaoruko-levels of awesomeness by standing up to a Bad End effect and not having her energy drained and doing so flocked by an army of forest animals. Nothing is mentioned of her ever again.
Kolulu from Zatch Bell! could've learned to control her powers and be an additional ally for Zatch, as well as a potential love interest, however Kiyo had Zatch burn her spell book and send her back to the Mamodo word early on.
Though most of the characters are hired by Fumito to act as Saya's "friends", Tadayoshi Kisaragi is the only character who has been under Fumito for a long time and he's a half-human, half-Elder Bairn. It would be interesting how much he has been under Fumito before the events of the TV series. Only those who have read Blood-C: Izayoi Kitan would know what he is before he worked with Fumito and sadly, that manga hasn't been licensed or scanlated yet.
Yuka, who is one of Saya's classmate and happens to be 28 years old who participated in the experiment so she can be the governor of Tokyo and doesn't really care about the gruesome events in Ukishima. She even appears in the movieas being one of the survivors from the TV series except that she only has two scenes where she eventually got her wish in the end. It would have been interesting on what kind of role did she contributed to Fumito's organization and possibly, her interaction with Saya if only these two ever meet again.
In the movie also, asides from Mana and Kuroto, the rest of the SIRRUT members have some interesting personalities but they don't have much background which makes you doubt about them being resistance fighters against an organization with a private army and the capability of creating and controlling human-eating monsters.
Fullmetal Alchemist has an annoying tendency to do this to its female characters. Paninya and Sheskadisappear entirely soon after they're introduced, Lan Fan gets Put on a Bus (though The Bus Came Back), Lustgets killed off while the other Homunculi last until the finale, and while May and Olivier have plenty of moments to shine they get nowhere near the pagetime/screentime that the male characters in similar situations get. Even Winry, supposedly a main character alongside the Elric brothers, constantly gets shoved to the side and forgotten about, though she's at least understandable as she's not an alchemist, soldier, or combatant of any kind.
Tsumugu Kinagase of Kill la Kill. In his first appearances he was portrayed as some sort of badass secret agent, being able to subdue Ryuko without any powers but only through superior tactics. It was implied that he fought against the Kamui because one of them absorbed his sister. Later on, after the reveal of Nudist Beach, who he was a prominent member of with Aikuro, all of his badassery was removed bit by bit until he became little more than a grunt in a different outfit who sometimes didn't even have lines. To top it off, the backstory of his sister being absorbed by a Kamui was Left Hanging, and it was never explained who he was or what the deal of his pact with Aikuro was (not that Aikuro's backstory was all that fleshed out).
Kagerou Project's Kosuke Seto. Despite being part of the original founding trio of the Mekakushi-dan / Blindfold Gang and his connections to resident gorgon-girl Marry, not much of his character or past has been explored aside from the fact that he was raised in the same household by Ayano and a song detailing his first encounters with his powers (which was a bonus track, mind you). Mekakucity Actors is trying to rectify this by giving him more screentime, but even then his character is not explored much.
Similarly, Kuroha during his time in the anime. He is briefly seen in the opening and episode 11, and during The Stinger of episode 11, he is hyped up as a main source of conflict in the next episode. Come episode 12, he appears for all of five minutes before Shintaro and Ayano step in to thwart his plan. He dies in the Daze not long after.
Shamrock, Marvel's Captain Irish heroine. She's possessed by the spirits of dead Irish soldiers who have unfinished business. When they possess her they give her the speed, strength and martial skill of a thousand dead warriors... oh sorry, they actually made her really, really lucky. But wait, it gets better; she retired from superhero-ing to become... a hairdresser. And no one cared!
Cute Mute and Body Surfer Jericho. After being stuck on a floppy as a Brainwashed and Crazy ghost for a couple years he was finally revived and restored to his old self and with a new body... only to be shoved into limbo about ten issues later where he would turn up a in couple years evil again due to multiple evil personalities from his power of possession (and also possibly from being 'dead') and ultimately suffer Eye Scream. What makes this even more of a waste was that during Jericho’s short time as a newly revived hero, he had hardly any interaction with any of his old friends (especially best friend/almost love interest Raven who resurrected him but instead their relationship seemed forgotten) or a decent reunion with his father Deathstroke the Terminator, or really anything about the character was explored besides "mute son of Deathstroke". Now, the mute part has been taken away, thus DC Comics having one less hero with a physical disability. Besides some sweet bonding moments with his half-sister Ravager, Jericho was mostly stuck in the background and underused until he was thrown in to the mediocre and forgettable stories DCU: Decisions and the Titans/Teen Titans/Vigilante crossover Deathtrap. However, as of Blackest NightJericho seemed to have recovered from both insanity and Eye Scream... for now.
Several fans of the modern Superboy, disappointed at his editorially mandated shock death in Infinite Crisis, were perked up by the reveal that his evil yet sophisticated clone Match would finally be made part of a teen villain team alongside fellow evil clone Inertia. Since Match had previously infiltrated Superboy's close circle of friends and had successfully manipulated them and even gained a villainous crush on Wondergirl thanks to his high degree of intelligence, it was hoped he'd be an epic villain and we'd get to here some great monologues. Then the team finally appeared. Match was a carbon copy of Bizarro. No real characterization. Weaker power level. And redundant; a Superboy Bizarro had already been done.
Toxin in Spider-Man. He was introduced in the Venom vs. Carnage series as being basically a good counterpart of Spider-Man's villains Venom and Carnage. The character became an Ensemble Dark Horse amongst some fans, and could have been quite interesting, having his own conflict and a unique relationship with his symbiot. But all he got was a short-lived limited series where he fought mostly villains that weren't really able to match him (his main antagonist, Razor-Fist, was just a guy with blades instead of hands. Against a guy with Venom's and Carnage's abilities combined), and was never actually seen again after that. When the symbiote finally showed up again, it was stripped from its original heroic host, Brainwashed and Crazy and forced to bound with a Eddie Brock to go kill the Flash version of Venom.
This is pretty much the premise of Avengers Arena, killing off teenaged heroes with cult followings in a Hunger Games style fight to the death. Because the characters originated in series that had been cancelled though, they fall into C-List Fodder box described above. Detractors reaction has pretty much unanimously been "You could have brought the characters back another way and considered reviving their series instead of killing them in cold blood, damn it!"
During the Fantastic Four story arc in which Franklin Richards was sent to the distant future then came back with a Plot-Relevant Age-Up, Marvel seemed to bend over backwards to make sure the adult Franklin never encountered Rachel Summers, the time traveler who was his girlfriend in her own alternate future. Then when the arc was concluded they promptly erased the adult version of Franklin from existence and brought back the child whose lack of control over his powers means his only way to participate in stories is as a either a kidnapping target or a source of Deus ex Machina. At least the aged-up version was an actual character.
Reed's father Nathaniel, who became a warlord in another dimension and fathered the warrior woman Huntara, got summarily retconned as just an alternate universe version of Reed's real dad, and then killed off-panel. A completely different character was then introduced as Reed's "real" dad.
Kryptonian criminals and Abusive Parents Zod and Ursa had their young child end up on Earth, where Superman and Lois Lane adopted him under the name Christopher Kent. The Character Development and story potential opened up by Clark and Lois finally becoming parents was then wasted when Christopher got sucked into a Year Inside, Hour Outside dimension for a Plot-Relevant Age-Up and wound up becoming just another minor character by the "New Krypton" arc. Especially sad as the New 52 reboot came not too long after all this, so Christopher's change to the status quo would not have been permanent in any case.
This was particularly bad in Archie Comics' Sonic the Hedgehog during the Penders/Bollers era as many characters were introduced, especially by writers other than the two, then dumped as the two did their own things.
During Spider-Man's poorly received "The Other" storyline, a subplot involved him fighting a new villain named Tracer. Tracer at first seems completely forgettable, literally just a punk with a gun, but he is later revealed to be a robotic entity that claims to have arisen from the internet as a sort of god to the world's computers (like Marvel's very own version of Lain). He gets destroyed, but declares that he'll be back. He hasn't been back.
The otherwise pretty forgettable Quasar spinoff Star Blasters introduced an alien robot villain named Skeletron. He claimed to be the sole survivor of an ancient race of machine creatures called the Turgentine Technenium, who had dominated a huge swath of the Marvel Universe eons ago, only to finally be destroyed in a tremendous war with the organic races of that era. He got killed, and the Turgentine Techenium hasn't been mentioned since.
In The Prayer Warriors: Battle With the Witches, Voldemort appears in a single scene, establishing himself as an enemy to both the Prayer Warriors and Hogwarts, and blackmailing Draco into killing Michael with the threat of killing Ebony so that he will be able to continue to fight against Dumbledore. It would have been more interesting to have an additional opposing faction, but Voldemort is never seen again.
Film — Animated
The Furious Five in Kung Fu Panda. Wonderful character design, awesome powers, voiced by the likes of Lucy Liu and Jackie Chan, each with the potential for intriguing backstories — but for such an imaginative, talented group of characters they seem remarkably underutilized. However, they're given a bit more to do in the sequel (particularly Tigress) and are also fleshed out a bit more in supplementary material like the Secrets of the Furious Five special and the Legends of Awesomeness series.
Brutus of The Secret of NIMH has a scary introduction where he menaces Mrs. Brisby with an electrified spear, but that's his only appearance in the film. He's apparently in the scene where the rats are moving Mrs. Brisby's house as Justin shouts for him, but he's not on-screen. A scene of him actually getting to use his badass electro-pike (against Dragon, perhaps?) would have been nice.
Zee from Monster House. At first she's a nasty (though darkly humorous) subversion of the sweet and kind babysitter, but there are a few moments here and there that suggest she's not altogether bad and there's even some build-up as to her involvement in the titular Monster House (at one point she offers to go and see what DJ is so afraid of). Given the emphasis put on her in the film's first half, many Genre Savvy viewers expected her to turn up again in a Chekhov's Gunman capacity, but ...nope. Instead she disappears halfway through the film and only reappears for a tiny scene during the closing credits.
Valka in How To Train Your Dragon 2. She's shown to be an incredible character with a connection to dragons, a sympathetic backstory, and a very spooky design aesthetic that is great to look at. But then she gets pushed to the sidelines for the sake of Hiccup's character development, and in a situation where you'd think she'd do great, she ends up being pushed down almost immediately.
The third film is lousy with this, wasting not only Colossus, but Psylocke and Multiple Man as well. Even Callisto could have gotten more characterization mileage than simply being another of Magneto's lackeys. Basically, there are two kinds of characters in the third film: on one hand, you have the characters who could all be the poster children for this trope. On the other hand, you have Wolverine.
Darwin, who was shown to have useful powers and a fair amount of character potential, falls victim to Black Dude Dies First in a relatively minor conflict well before the final showdown. Despite the fact that his power is specifically that he can't die and there is literally no reason given for why he did.
Riptide and Azazel, two of Shaw's minions who join Magneto after he kills Shaw, are quite popular among the fans, some of whom even ship them. Even their actors were interested in their return in X-Men: Days of Future Past, Alex Gonzalez saying in an interview that he'd "really like to be in the sequel" and explore more of Riptide's powers, and having signed on to play him in one or two more films, while Jason Flemyng said he was interested in exploring the origins of Azazel's son, Nightcrawler. Yet plans for the Hellfire Club's return were dropped when the writers chose the Days of Future Past storyline, Riptide gets a glorified cameo and Azazael gets killed in-between movies.
Wade Wilson/Deadpool. After getting the chance to display a weary snarky persona, he's taken out of the film until the climax, where we see that Stryker has basically turned him into an Humanoid Abomination. With his mouth sown shut, essentially robbing him of the sole trait he had in the movie.
Comic fans had been calling for Gambit to show up in the movies since the first X-Men film. When he finally does here he's little more than a built-up throwaway gag.
Cyclops, leader of the X-Men and arguably the REAL main character of the comics: the guy was less than a cameo. The character had to deal with the death of his lover, but apparently that wasn't worth exploring, nor were his, you know, actual leadership abilities. Also, with Xavier's death, the idea of Cyke taking leadership of the X-Men as a whole and not just the field team was very doable (he's been leader of the majority of the mutants for years in the comics), and would've made sense in the context of the story. But no, he was thrown out like yesterday's trash just so Fox could have more of the eternally overrated Wolverine.
The only mutants in the future who get any meaningful dialogue are Xavier and Magneto, with the rest essentially being glorified cameos, even established characters like Storm, Iceman, and Kitty Pryde. This is mostly a result of several scenes cut from the film in order to keep the runtime short.
Those hoping for more of the First Class mutants in future installments had their hopes dashed when nearly all of them were killed offscreen. Unless said characters are revealed to be Not Quite Dead (which certainly could happen with Emma Frost as she was not among the autopsies of confirmed dead mutants) or come Back from the Dead, they aren't going to be used again - which is a bit strange when you consider that this movie resurrected every other character.
General Grievous got maybe ten minutes of screen time in Revenge of the Sith, and spent it threatening random underlings, running away, and getting killed by Obi-Wan in one of the worst anti-climaxes of the entire saga. This is especially hated by a lot of fans as the (very popular) Star Wars: Clone Wars series had already established Grievous as a monstrousJedi-killingOne Cyborg Army, and then the film comes along and turns out that nope, he's a coward with a nasty cough.
The Phantom Menace has Darth Maul. He was dark, energetic, had strange markings and gave two Jedi an even fight, managing to kill the more experienced of the two. He got two or three linesnote many droids got more lines than he did, and not even just C-3PO in the entire movie, no characterization except for a brief mention of wanting revenge on the Jedi and then got killed because he apparently couldn't believe that Obi-wan could make that jump. It's a slight consolation that Star Wars: The Clone Wars spent a few episodes on his origin and gave him another chance.
Attack of the Clones has Jango Fett. Seemingly his entire existence is owed to the Ensemble Dark Horse power of Boba Fett (of whom he is revealed to be the "father"), so nothing is known about his motives or past or what he's doing with the Separatists in the first place. While he does get a chance to show off some cool moves, after being on the receiving end of a deadly Curb-Stomp Battle he's never mentioned again.
His son, Boba Fett, also gets this, and is famous for it. After all the build up in The Empire Strikes Back, at the start of Return of the Jedi a blind Han accidentally hits him in the back with a stick and he falls into the Sarlacc pit.
Count Dooku left the Jedi Order in protest of their support of the horrifically corrupt Republic, and eight years later reemerged leading a separatist movement of systems that thought the same way and wanted to form their own government, backed by a bunch of Mega Corps who had the military muscle to ensure the Republic would agree to their terms. Any potential for him to be a Well-Intentioned Extremist is shattered when he's swiftly revealed to be an evil Sith Lord, and his pitifully small screentime means he doesn't even receive any character development, ultimately getting killed off unceremoniously in the first ten minutes of Revenge of the Sith. It's telling that one chapter of the RotSnovelization (which portrays him as a multiple-level Fantastic Racist intent on forming a Sith Army) gives him more focus than anything in the films.
As David Morgan-Marrants about, Zam Wessel is exposited to be a Shape Shifter. This affects nothing of any part of her screen time, and nowhere in that movie or the next does the franchise exploit potential for that revelation. Not even the Expanded Universe manages to exploit that detail nearly as well as they should.
There are tons of Transformers in the films that get the shaft and become disposable mooks on both ends of the war. One of the reasons could be because it's a Human-Focused Adaptation. It's more glaring because of how many past versions of the franchise there have been - everybody is someone's favorite from a past series, and the overwhelming majority wound up standing around doing nothing if an Autobot, and easily got ripped to shreds in two seconds if a Decepticon, and only has a personality via Memetic Mutation (Bonecrusher hates everything) or the comic book Expanded Universe that is generally seen as a big improvement over the movies themselves. You just don't have the likes of Sideways or Shockwave around and give them all of thirty seconds of screentime that could've been filled by any nameless generic Red Shirt... unless you're the movie writers.
Taken 2: Murad could have been a sympathetic Anti-Villain as an avengingPapa Wolf if more time had been spent on showing his relationship with his family, including the late son he's avenging, as well as keeping it professional. Redshirt deaths were inevitable, and we could have tolerated the torture of Jean-Claude as fair payment for what Bryan had done in the first film. He could have shown that Bryan's didn't have to be the right way and injected some moral ambiguity. However, he quickly proved himself every bit the scumbag his son had to have learned from, and then there was no turning back.
Halo 4: Forward Unto Dawn builds the backstory for young Thomas Lasky, future Captain of the UNSC Infinity, who learns to shoulder responsibility in the face of doom thanks to the example of Master Chief. As for his supportive best friend Chyler Silva, she gets promoted to his girlfriend for forty minutes before getting abruptly Stuffed into the Fridge. Halo 4 then introduces Sarah Palmer, the chief officer of the SPARTAN-IV Program who is alsoThe Lancer to Lasky. Rather than relegate Chyler to be a sudden casualty for Lasky to mourn over, why not have had her also learn to become a great leader and become the lead Spartan of the UNSC? That would have allowed them to also continue their relationship formed in Forward Unto Dawn.
The ninth Friday the 13th film, Jason Goes to Hell: The Final Friday, reveals that Jason Voorhees has a sister. But instead of using this to tell the audience more about Jason or Voorhees family's backstory, her role in the film is to be killed by him, and having her corpse to be conveniently present for the climax.
The Other in The Avengers. Although he is established at the beginning as the servant of a greater villain (revealed at the end to be Thanos), he is quite shadowy, sinister, and enigmatic in that he is original to the film series. He merely serves as communication between Loki and Thanos, and messenger to the latter.
Lady Sif, brave, beautiful, bad ass goddess of war from Asgard played with verve and gusto by Jaimie Alexander, is woefully underused in both Thor films, despite being an important character in the comics. At least she gets the honor of being one of the few movie characters to make an appearance in Agents of S.H.I.E.L.D., and most fans\reviewers agreed her appearance practically made the episode.
Malekith the Accursed in Thor: The Dark World never managed to be more than just a Generic Doomsday Villain. What makes it painful is that he's played by Cristopher Eccleston and he was originally supposed to have more screen time.
Joe Brody, who is regarded by critics and fans as the movie's best human character, dies in the first third of the film. His son, Ford, who replaces him as the human protagonist, is viewed to be less interesting by comparison.
Godzilla himself never gets a real appearance until the final act, with the Mutos driving most of the plot and is only present to combat the creatures' existence.
Vivienne Graham's character also has shades of "They Wasted a Perfectly Good Actress," since she doesn't have much to do except help Serizawa with plot exposition.
The English writer and literature historian George Saintsbury wrote of Éponine Thénardier in Les Misérables, claiming if "Hugo had chosen to take more trouble with her, might have been a great, and is actually the most interesting, character." Some adaptations (such as the Film of the Musical) cast an actress good enough for Éponine to become an Ensemble Darkhorse.
Leah is an Iron Woobie. She's trapped in a telepathic connection with her ex-boyfriend (who she shared a fulfilling relationship with before he Imprinted on Emily, Leah's cousin, and promptly ditched her) and a group of various people who all hate her because of her bitterness about the above. She's one of the few female characters who actively seeks freedom and independence, and she can transform into a wolf. Once Jacob's rebellion against the Quileute pack gives Leah an opportunity to escape the pack's mental link, she runs with it, leaving her family and protecting the vampires she detests, solely because doing so is more tolerable than being in Sam's proximity. (This is also around the time that she Takes A Level In Kindness and bitches out Bella for her cruelty to Jacob.)
Seth is a badass warrior, one of the series' few characters to be truly compassionate, and the only werewolf who doesn't hate vampires simply for existing. His main purpose in the narrative is as a sounding board for more angsty, pessimistic characters, and we don't get an idea of his perspective outside of that.
Rosalie Hale, Rich Bitch vampire with a distaste for Bella that many readers can sympathize with. (She's also hinted to be a Tsundere behind the scenes, and is one of the few vampires to see value in human lives.)
Jasper is seen as a favorite amongst many: a battle-hardened vampire who was alive during the American Civil War and is now trying to become a better man due to falling in love with Alice.
Bella's father Charlie is also fairly popular among the people who otherwise generally don't like the series. Mostly it's the fact that he's one of few characters who seems to have real-world responsibilities and friendships, and the fact that, especially in the early novels, he openly distrusts Edward.
In The Riftwar Cycle the author devotes a book to novelizing the plot of the insanely successful RPG Betrayal at Krondor written by Neal Hallford and set in his world. One of the characters, Owyn Beleforte, ends up as a very powerful 19-year-old magician who has become friends with one of the allegedly Always Chaotic Evil dark elves and the first character to actually sympathize with the enemy. Additionally, he can understand their language due to a spell cast on him by one of their witches. He's also one of the handful in the world to be aware of the nature and location of the Artifact of Doom after helping save the world from it, as well as the super secret details of the last major war between humans and dark elves - to wit, the dark elves were manipulated by a third party into a near-suicidal invasion that killed many of them off like flies. Oh, and his dark elf friend dies through a Heroic Sacrifice. The story that practically begs to be told is that of Owyn taking up his fallen friend's cause and working further toward the peace which neither of the nations really want at the moment - he is unique in having both the backstory and motivation as well as the power to make feasible progress in it. The author, however, holds no interest at all in a character he didn't come up with, so after that book Owyn allegedly gave up the life of adventure and went home to live a normal life - according to Word of God - his fate didn't even get an in-story explanation, much less an appearance on-screen.
Fans will never agree on it, but it seems that the decision to kill Anakin Solo just as they'd launched three major plot arcs around him (romance, check; special abilities, check; unique connection with enemy culture, check) was a bit of a dead end. Not to mention multiple Force prophecies about Anakin's future importance (some dating to well before the New Jedi Order era) that never played out. Oddly, the writers of the post-NJO era seem to agree, as they keep making everyone relive his death. Oddly, Anakin bordered on Creator's Pet in the Corellian Trilogy. According to the writers, they were going to make Anakin the hero of the NJO books, but George Lucas vetoed it because he was afraid people would mix up Anakin Skywalker and Anakin Solo.
Jaina Solo as well, since the writers turned her into a Flat Character.
Also, Anakin's girlfriend, Tahiri Veila, gets this; while she was important for much of the New Jedi Order, she got Demoted to Extra in the last book and then hovered around in the background for a while, as if the writers were unsure what to do with her - and then brought her back into the spotlight only to have a lot of her Character Development undone so she could be derailed into a villain.
Brian Jacques is guilty of this quite often in the Redwall series, introducing a charismatic, kickass new character and then killing them off within two chapters. Has overlapped with Too Cool to Live.
Did anyone else plod through Brisingr just hoping that Eragon and Roran will go away so we can have more Nasuada chapters? It's amazing how awesome and realistic she becomes, probably because Paolini makes her problems practical concerns rather than the philosophical, "deep" issues he tries to have the others grapple with.
There were a few of these types in Animorphs, most notably Joe Bob Fenestre from The Warning and Arbat-Elivat-Estoni from The Arrival. David might count as well, given his much-anticipated return to the series was much less climatic than the fans were hoping for.
Remus Lupin, Nymphadora Tonks, Luna Lovegood, Mad-Eye Moody, Peter Pettigrew, the Hogwarts professors besides Dumbledore & Snape (not to mention the trope namer for Hufflepuff House, and Ravenclaw doesn't get much more exposure)... if we all thought up a character whose development we might consider to be short-changed and compiled them in one place, we'd probably have enough guests to hire out an entire restaurant for.
Despite being a pretty major character, Professor McGonagall has also been seen as this after Rowling revealed her terribly depressing backstory on Pottermore.
Theodore Nott, despite only being mentioned a few times a lot was revealed by Rowling about him. Apparently he's the son of one of Voldemort's early Death Eaters and is just as pure-blooded as Malfoy. He is very similar to Malfoy only Nott is not part of a Slytherin gang and may be even cleverer than him. He could've served as a foil to Malfoy but unfortunately he was almost completely cut.
With the exception of Spink, all of Nevare's academy classmates completely disappear from the story after the first book of The Soldier Son. Especially Gord and his troubled relation to Trist seemed to have loads of potential, but they are never seen again.
Mary Watson, née Morstan, in Sherlock Holmes. Despite playing a major role in The Sign of Four, having quite a bit of genuine detective skill herself, and ending up married to Dr. Watson, she's never used again except in cameos, and during the Time Skip between "The Final Problem" and "The Empty House", she's killed off.
Cinna. One of the first things established about him is that he volunteered to be the stylist for the District 12 tributes despite it being a traditionally unwanted job, but we never find out why. Or why he doesn't have a Capitol accent, or why his fashion sense is so understated as compared to the rest of the Capitol, or... anything about him really.
Johanna once says that the mimickery of the Jabberjays can't hurt her because everyone she loves is dead - we never find out why. She also barely appears in the third book.
Rue also doesn't get much characterisation - just enough to make her an appealing victim. Thresh got it even worse.
Nor does Prim. As the sister of the main character, and a huge motivation of Katniss' actions in the first book, you'd think some insight into her personality and their relationship would be shown.
Lavinia, the red-headed avox girl who Katniss and Gale saw escaping from the capitol. We're never told why they were running, how they got to district 12, or anything of the like, and she's promptly killed off with almost no part to play at all.
The girl from District 4 was the only member of the career pack in the first book to not have any form of personality revealed and is killed early on. In the film she wasn't even a member of the pack and was killed early on.
"Foxface". Some of the other tributes from the 74th Hunger Games that remained nameless throughout the first book had their names revealed in the second, but despite being built up as a potentially interesting character in the first book, her real name is never revealed and the victors' trip to District 5 is completely glossed over in Catching Fire.
In Perry Moore's Hero, the protagonist Thom gets picked up at a gay bar by a slightly older young man and has his first kiss with him. Later, it's revealed that Thom's would-be beau is the supervillain Ssnake, who stands accused of murdering a beloved superhero at the time this was happening. When Thom reveals this to the public, it sets in motion a series of events that lead to the real villain's downfall and saves the planet from destruction. But sadly, we never see Ssnake again, even though he could have been a much more interesting love interest than Goran.
Clawface is one of the earliest in the series. He was formerly one of Graystripe's idols, but turned out to be an unrepentant villain. He also murdered Firestar's love interest Spottedleaf in cold blood, and he was the only character in the series capable of making Firestar completely lose it and try to kill him (which happened whenever Firestar so much as saw him). As well, prequel novel Yellowfang's Secret revealed that he was Yellowfang's sister's mate, and brother to Nightstar, the leader of ShadowClan after Brokenstar. Despite this, his personal connections to the characters are never explored, and after he's killed in Fire and Ice he's never mentioned again. Even when the entire fourth arc revolved around the past villains making a comeback after their deaths and he was confirmed to be among them, he never actually appeared in the series.
Brokenstar is possibly an even bigger wasted character than Clawface. He's supposed to be the villain of the first book, and has one of the darkest plots in the series: use Child Soldiers to make his Clan larger and stronger than the others, then sweep through them and destroy them so that he can be in charge. Also, he managed to drive out an entire Clan, a feat which no one has ever been able to replicate, and he has another Clan completely subservient to him. Despite this, he's never written as a real threat, and gets overshadowed by the much more generic Tigerstar. Even his eventual comeback didn't help him.
Jingo and her crew. A Clan-like group facing their own struggles in a city and harbouring a grudge against Sol? Would be cool if they'd so much as been mentioned since their introduction in Sunrise.
Gaunt's Ghosts, true to its Anyone Can Die nature, is filled with people with interesting personalities or histories, or could otherwise have had a huge impact on the story, killed off unceremoniously without warning. Perhaps the most galling though is Colonel Wilder, Reasonable Authority Figure who managed to keep the Ghosts together and become their new commanding officer after many of the main characters are presumed dead, who is killed off in the very book he's introduced in.
Stevie Rae, a compassionate Wide-Eyed Idealistwho is killed early into the story, resurrected through dark magic, and becomes the disillusioned leader of the red fledgings. The glimpses we get of her descent of insanity (and eventual climb out of it) are quite interesting.
Speaking of Stevie Rae, a whole novel could be written about the red fledgings (outcast from everything they've ever known, seemingly abandoned by God, yet staying sane and retaining their personalities...).
Live Action TV
A lot of early boots on Reality TV shows, game shows or otherwise come off as this way. See also Shocking Elimination; some people who seem genuinely good at the game or are actually good in talent shows wind up eliminated early, sometimes for the wrong reasons, sometimes for being the low-man on the totem pole.
Brian and Annie in the American version of Big Brother. Season 12 (where Annie was from) is probably one of the smartest players in a season full of already-educated and genre savvy players. (Even if some players were Genre Blind; they were pretty booksmart.) Brian meanwhile was actually considered a legit threat; there's a reason Julie Chen spoke to him more than she did the other early boots. Alex and Parker from season 9, too, were booted mostly for the wrong reasons.
From Survivor, we had Dolly from Vanuatu, Marisa and Betsy from Samoa (Russell actually voted them out because he said that those two could have beaten him), then Sugar, Stephanie, Tom, and Cirie in Heroes Vs. Villains.
Tony by the end of the series. Season five killed his wife off at the very beginning, which had a potentially intriguing storyline that could have major ramifications, namely, after the man behind her death (Christopher Henderson) was exposed, just how far would he go for revenge? Instead, he spent most of the season offscreen in a coma. Then when he finally awoke he was then immediatelykilled off. And amazingly enough, it actually got worse when they retconned him back to life two seasons later. For his return we were given a massively convoluted revenge plot that mostly relies entirely on coincidence that concluded with one of the biggest AssPulls in the series.
The fifth season Big Bads, The Circle of Black Thorn, are introduced and killed off in just two episodes.
Doyle. Arguably he needed to die in order to give Cordelia her powers as a seeress, but watching the dynamic between Angel, Doyle and Cordelia in those first few episodes... damn it makes you wish that they'd kept him around. (Unfortunately a case of Real Life Writes the Plot, the producers getting increasingly worried about his drug problems.)
Whistler, the mysterious agent of the Powers That Be. Like the Doyle example above, the writers did have further plans for the character (in fact, Doyle was originally supposed to be Whistler), but the drug problems of the actor made this impossible.
Back in season 1, 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.
Victor started out as a cool recurring villain. He was an excellent Shadow Archetype to Michael, he and Michael shared loads of Ho Yay, he was an awesome Deadpan Snarker, and he was played by Michael Shanks. Naturally, when Victor and Michael teamed up, he died.
Tricia Helfer's fantastic villain Carla - another one who is offed way too soon.
Daniel Purcell is built up at the beginning as a central figure that the season's story revolves around but ends up succumbing to a whirlwind case of Face Heel Revolving Door and gets shoved to the background of the central story before finally having his arc petering out in the end.
Claire Maddox is presented as a foil for Patty Hewes but there ends up not being that much interaction between the two and she ultimately only appears in half the season.
Wes Kulick undergoes a pretty strong character arc and we're offered a lot of tantalizing hints about his past and the finale seems to set up some sort of storyline between him and Patty. Sadly, Olyphan took a lead role in Justified and sat out season 3 save for a small appearance in the finale.
Desperate Housewives: Lynette's horrible mother marries a wealthy but bad tempered, elderly racist. Normally the viewers would be eager to see the back of him except for two things: he was hinted to have Hidden Depths during the lead up to the wedding and he was played by Larry Hagman. He dies less than halfway through his second episode without the writers doing anything with him - the writers simply wanted an excuse to make Lynette's mother rich, ignoring the potential the character had in his own right.
This could arguably apply to the Doctor a couple of times:
For all the mixed feelings that fans have about the TV movie, most agree that the 8th Doctor was a fine character, and we should have gotten more of him. The new series begins with him already regenerated into the 9th, making him a case of We Hardly Knew Ye (though there are novels, comics, and radio plays he features in).
The 6th Doctor, who was supposed to start out as an abrasive, egotistical blowhard before softening considerably as his tenure went on. Executive Meddling cut his time short, so he never really got past being an abrasive, egotistical blowhard. Like the above example, there is Expanded Universe material that helps rectify this.
The Seventh Doctor's arc, as well as his transition from the Lighter and SofterFun Personified figure the execs wanted into a intelligently-characterised Machiavellian Knight Templar, was just really beginning to kick off when the show got cancelled. Like with the above examples, the Expanded Universe finished off his intended arc and did a lot more with him besides, while providing the low-censorship environment which allowed him to be one of the Darkest and Edgiest Doctors of them all.
Susan. According to Carole Ann Ford, she was promised when she accepted the role that Susan would be a weird, inhuman, telepathic Action Girl. The first episode is named "An Unearthly Child," and it turns out Susan is who it's talking about. Instead, we ended up with the original Screaming WomanLoad, who remains one of the worst examples of the stereotype in the show's history.
The ever-so adorable Amelia Pond, whom the audience is introduced to for about the first 15 minutes of "The Eleventh Hour", praying to Santa to send someone to fix the scary crack in her wall. She is smart, brave, witty, so incredibly likeable and huggable... then the Doctor gets in the TARDIS for a short hop of five minutes, and when he re-appears, Amelia is now 19 years old and has become a lot more jaded at the failed re-appearance of her Raggedy Doctor for all these years. Sure, Amelia is shown a few times, but it's only ever briefly, and usually in flashback or the sort. A lot of fans believe she would've made an excellent companion, but for the fact that the BBC could never have allowed a 7 year old girl to run off with a madman in a box across the universe.
Kamelion, the shapeshifting robot. Besides his inhuman nature, he was supposed to be unpredictable due to his weak will and prone to getting subverted by villains (particularly his former owner, the Master). Unfortunately they had the bright idea to build an actual robot (instead of just using an actor in silver makeup) and the only guy who knew how to to operate it had a sudden case of the death, so Kameleon ended up mothballed in a room in the TARDIS. Eventually they employed an actor in silver makeup just so they could kill off Kameleon and tie up that plot thread.
The Rani. Smart, capable, obsessed with dinosaurs, and acquainted with both the Doctor and the Master. A villainous female Timelord with elaborate plans, a functional TARDIS and a planet under her rule. She was a completely different type of villain from the Master; a villain who didn't care about power, just scientific knowledge, but was willing to go to sociopathic lengths to gain it. Used a total of two times (three if you count Dimensions In Time as canon).
Speaking of underused villainous Time Lords, there was the Meddling Monk from way back in the First Doctor episode of the same name. He was a rogue Time Lord, the first other than the Doctor and Susan to appear in the series (long before the names Time Lord or Gallifrey even became canon), who wasn't evil per se. The Monk just wanted to use time travel for his own personal profit, with the occasional reckless but benevolent scheme to try to change history for the better, like trying to cause the Industrial Revolution to happen early by preventing William the Conqueror from invading England. He would have been a great recurring adversary, and was used quite a bit in the spin-off media, but in the TV show he only appeared again once in what amounted to little more than a cameo.
Canton Everett Delaware III: a Badass Normal maverick FBI agent who answers directly to the President of the United States, proves instrumental to dismantling an alien conspiracy to control the United States government, and is engaged in an interracial same-sex relationship—in the 1960's, no less—that he defiantly refuses to keep secret. The Doctor apparently respected Delaware enough that he was one of only five people that he told about his impending "death"—the other four being Amy, Rory, River, and himself. Despite all that, Delaware gets no appearances beyond his introductory two-part episode, and the vast majority of his three-month battle with the Silence happens offscreen.
Due South: Ray Vecchio, in the series finale. Many viewers wanted him to be with Fraser in Part 2, not in Chicago and flirting with Stella.
EastEnders: Becca Swanson. An incredibly hot, manipulativePsycho Lesbian with an obsessive crush on Stacey Slater. Largely manipulated things from the sidelines and played a key role in the death of Stacey's husband, Bradley. Set herself up as Stacey's best friend, comforting her and driving a wedge between Stacey and her manic depressive mother, Jean with plenty of Les Yay between her and Stacey thrown into the mix. Then just as it looks as though Becca's plans are coming to fruition, Jean suddenly plucks up the courage to tell Stacey that Becca caused Bradley's death. Stacey slaps Becca who smashes Bradley's urn then just leaves without a fuss. She was a lot more interesting than a lot of antagonists on the show and was part of just about the only interesting plot they had at the time but both it and her just stayed in the background. It's like the writers deliberately thwart their own opportunities. They could have saved her for a fiery Christmas Day denouement.
ER had a tendency to introduce numerous new characters each season and maybe—maybe—keep them around for a while to see how they fit in with the rest of the cast. Two characters who stayed around the longest and were popular with viewers were Dr. Donald Anspaugh (John Aylward) and Dr. Lucien Dubenko (Leland Orser), neither of whom were even offered a spot in the main cast.
Ryder was introduced in season 4 as one of the newcomers to the glee club; however, unlike the others, he wasn't a bland expy of previous members, and had a very interesting character arc that the audience felt identified with, particularly being sexually assaulted by his babysitter at an early age (on the grounds that male statutory rape isn't represented as much as female on television), and a storyline that seemed headed towards being paired with Unique. However, season 5 decides to shove him and his character development to the background and never speak of it again, instead choosing to put him in a Love Triangle with Marley and Jake for no adequately explained reason.
Grey's Anatomy: Season 9 has Cristina befriend the attending Dr. Thomas (played by William Daniels), who is her new teacher. They don't get along at first, but she learns that she can learn a lot from him and she starts defrosting again. They engage in Snark-to-Snark Combat. Because of his age, his job is in jeopardy, so she tries to help him out only for him to die during a surgery. A devastated Cristina goes back to Seattle Grace.
Elle. The 7th episode of Season 3 set her up for a Heel-Face Turn, only to abort it at the last minute. Then she starts a relationship with Sylar which seemed to be going well until he suddenly kills her.
Scott the super soldier from Season 3. He's given significant screen time in "Our Father", up to and including an explanation of his motives for participating in the program, which is a novelty in a show where characters do things for unexplained and inexplicable reasons. He is the first recipient of the perfected formula, neatly subverts With Great Power Comes Great Insanity, and is all set up to be a big player in the finale. Then the finale comes and minor villain Knox unceremoniously snaps his neck.
House of Anubis: Has many of these characters, many who are brought onto the show for one season then vanish into non-existence in the next. Jason Winkler, who people are still waiting desperately to return, was brought on as a sympathetic and likable character who was never mentioned again after the first season. Minor character Benji probably got this the worst, though, because he was on for a grand total of two episodes, and in that time got to flirt with Patricia, stir up an old rivalry with Eddie, and become a liked character- all to just disappear right after and was never mentioned again.
Justified: In Season 5 Jean-Baptiste is introduced as a Haitian alligator poacher, and right-hand man of prospective Big Bad Daryl Crowe. He's the Only Sane Man in Daryl's crew, has calm, but still menacing demeanour, and manages to make Danny back down from harrassing Kendall. And then what happens? Danny grabs a shotgun and performs a bridge dropping. One could make a good case that the season does the same thing to Sammy and Theo Tonin, longtime villains who exit the show with very little ceremony.
Kyoryu Sentai Zyuranger: Burai. Super-cool Sixth Ranger, the first real Sixth Ranger in Super Sentai in fact. Fan-loved and wildly popular, but after his initial arc he gets no development and very little interaction with his team-mates due to Living on Borrowed Time and having to spend most of the series offscreen in a Place Beyond Time. He was eventually killed after it looked like they'd be able to restore his lifespan, in order to generate cheap pathos and to give Geki, the red ranger, his Bling of War.
A case where it was not the fault of the writers was Eko, likely the most interesting of the tail section survivors who is unceremoniously beaten to death by the smoke monster with plenty of interesting story left in him. This was mostly due to the actor wishing to back out, despite a large character arc having been planned by the writers.
Could be said of some of the short-termers: Libby, Charlotte, Ilana, etc. Shannon got the bridge when she was just starting to develop.
Richard, the mysterious immortal agent of Jacob, gained a lot of Memetic Badass points with fans due to his mysterious immortalness, as well as his actor Nestor Carbonell's incredibly badass eyelashes. A lot of people wanted to see more of him doing many badass things, however the timing of the unveiling of the background and the fact that mysterious characters don't stay mysterious for that long if you spend too much time on them, meant that he only got the one focus episode and some side character action in the final season.
Frank Lapidus. Brief dialogue painted him as something of a conspiracy theorist (on a mysterious island with time travel and reality-bending numbers and polar bears! Imagine the possibilities!), yet he was never given his own flashback episode (yeah, he shared one with the other freighter people, but that hardly counts). His upgrade to full-time status in season 6 was also wasted, as besides entertaining snark, he didn't really have anything to do until the very end: somebody needed to fly that plane off the island.
Mash: Colonel Flagg. Appered in seven episodes over the show's eleven season (eight if you count Edward Winter's earlier role of Captain Holloran), and in his two or three appearances, he was something of a Bad Ass, and Hawkeye seemed genuinely scared of him. By his finale appearence in "Rally 'Round the Flagg, Boys", he was a bumbling fool tricked into trying to arrest the mayor and chief of police of Uijeongbu as communists after Hawkeye operates on a North Korean. Ironically, writer Ken Levine mentions they tried to avoid using him too often and turning him into The Scrappy.
The sorceress Nimeuh: an interesting villain with plenty of justification for her crimes against Camelot, an intriguing backstory with Uther and Gaius, and plenty of mileage left in her as a character before she is killed off at the end of the first season.
Aglain, a wise Druid who rescues Morgana and helps her come to terms with her magical powers, only to be unceremoniously killed off by Arthur's men when they mistakenly think he's kidnapped her. This was entirely intentional - the character was designed in order to show Morgana that her magic was not to be feared and that (at the same time) men like Uther are to be pitied for their stance on magic. Given how Morgana eventually turns out, one can only mourn What Might Have Been had Aglain lived to be her mentor.
Julius Borden, a One Shot Villain and amoral treasure hunter. He had a Dark and Troubled Past, was once a protegee of Gaius, had inside knowledge on dragons, was resourceful enough to collect the three pieces of a triskelion strewn across the country, managed to outwit Merlin and the knights, and to top it all off, was played by James Callis. The writers give us just enough on his background to get us interested, then simply use him as a device to get Merlin to a hidden tomb before killing him off.
"Identity Crisis" gave us FBI Special Agent Courtney Krieger, a rookie member of Fornell's team, who is tracking an arms deal. She proves to be quite resourceful in the investigation and trades phone numbers with Ziva, but she's never seen outside of this one episode.
The season seven premiere gave us a One-Scene Wonder named Heather Kincaid, a Seattle police officer who was applying for Ziva's old job with Team Gibbs. The character had a snarky personality and would have meshed with Team Gibbs better than any of the other applicants in the episode (it helped that her actress had good onscreen chemistry with Michael Weatherly). However, DiNozzo intentionally sabotaged her job interview at the last minute because he was still wangsting over Ziva's resignation, and we never saw Heather again.
In "Kashmir" they introduce a new minor character called Ashley, a girl fighting on the side of the rebels. Her very first scene depicts her sniping two militia soldiers in quick succession using a longbow, and later on we even learn a bit about her background. Sounds like she could even shape up to be a better version of Charlie. Unfortunately, she gets unceremoniously killed off toward the end of the very same episode]].
Nora Clayton, in "The Dark Tower". She had been one of the main characters who contributed something to the team, and she even rekindled her relationship with Miles Matheson in "The Love Boat". At least she killed off a lot of bad guys before she died in the first season finale.
Sherlock: Kitty Reilly, Mycroft's mysterious and snarky assistant "Anthea", John's Action Girl girlfriend Sarah Sawyer, and DS Sally Donovan. The first two are nowhere to be found in season 2, the latter seems to only be there to criticize Sherlock and be yelled at by Lestrade.
Stargate Atlantis: Elizabeth Weir. Despite being a lead for three seasons, having a bucketful of UST with the other lead John Sheppard, universally beloved by fans, and being a strong female character who depended on her brains instead of fighting abilities, she was given barely any character-centred episodes, minimal backstory and was Put on a Bus at the beginning of Season 4. Cue outrage.
Linea, the genocidal maniac who could hack computers, cure the blind, and create diseases that wiped out whole planets, who had a complete understanding of how the Stargate worked, and was an old lady, was such a cool villain for SG-1 to face. It was their fault she escaped from her prison, and she was obviously smarter than them. After her debut episode she came back a year later; younger, mindwiped, and redeemed so Daniel could have a rebound girl, and then was completely forgotten about.
Aside from Baal, Yu was by far the most interesting of the System Lords. He was the only one that was openly against Anubis from the beginning, was nice enough that his worshipers seemed to genuinely respect him instead of following out of fear, like Baal he recognised the value of not obliterating Earth, and was so old even by Goa'uld standards he was actually going senile. And yet with the exception of during a brief Enemy Mine situation none of this was really explored, and he went the way of all the other System Lords after the Replicators arrived.
Replicarter. She was effectively a robotic copy of Samantha Carter, but in control of the entire Replicator army. Think about it, all of the creativity and brilliance Carter uses to help the good guys, now applied to expanding an ultra-advanced machine race working to conquer the universe. Not to mention Replicarter's claims that she and the original are Not So Different, implying Carter possesses megalomaniacal inclinations. However, nothing ever comes of it. She appears in one cameo, then one episode to explain her origins and how she's evil. Then, she launches a massive invasion and annihilates the Goa'uld…and is killed off without any additional development, finishing the story as a Generic Doomsday Villain.
The tragically underutilised ship pilot Ensign Mayweather. Born and raised on a space freighter, he had the most practical space experience of the entire crew, despite his relative youth and low rank in Starfleet. The writers never seemed to grasp the inherent hooks of this however, and the poor ensign had more or less nothing significant to do during the show's entire run.
Malcolm Reed, who served in freaking Section 31 before joining the Enterprise crew. For the unaware, this is the branch of Starfleet that is roughly on par with MI6 in terms of undercover operations. In other words, James Bond was the weapons officer of this ship, and he wasn't even a part of the Power Trio.
Hoshi Sato, highly skilled linguist and inventor of the universal translator... who quickly got sidelined into pretty much the ship's errand girl for stuff Archer couldn't bother assigning to anyone else. Compare this to her Mirror Universe counterpart who in addition to being the Mata Hari, ends up becoming the Empress of the Terran Empire.
Tasha Yar, whose actress Denise Crosby complained about the lack of anything for her character to do on the show, and is the reason why she decided to leave the show and kill off her character. Having grown up on a dystopian failed colony she had the most unique backstory, very much antithesis to the Federation's utopian image. She was originally conceived by writers as Star Trek's answer to the very butch Vasquez from the very un-Treklike Aliens, but apparently writers just didn't know where to go from there since Trek at the time intentionally stayed away from war and confilct as plot elements. She came back temporarily in a very unusual plot twist and was eventually semi-brought back in the form of Sela, a Romulan Half-Human Hybrid. After lurking mysteriously for a few episodes, she comes out of the shadows, and eventually meets Picard and tells the story of how she came to be. Picard is adamant about not believing a word of it; we don't hear why... or any more of her story. We see her once more ever, in a role that any nameless Romulan commander could have filled. In the end, there was no point to setting her up like she was going to actually matter. It makes you wonder What Could Have Been if Denise Crosby had been cast as Counselor Troi and Marina Sirtis as Tasha, as originally envisioned, meaning that Troi would have been killed off and Tasha would have lived...
Then there's Tasha Yar's sister, who had a very memorable episode, with dimensions Denise Crosby probably wished Tasha had during Season 1 - doubles as a What Could Have Been had the writers later in the series been penning Season 1 tales.
At least one of these pops up per season: there's Meg's brother Tom in Season 1, most of the psychic kids in Season 2, Bela Talbot from Season 3, and so on.
Season 8 has Samandiriel, AKA Alfie, the angel who bargains for Kevin on behalf of Heaven in "What's Up, Tiger Mommy?" and one of the few non-Castiel angels to not be a huge douchebag. He's somehow captured by Crowley offscreen even though he's probably more powerful than him. After two episodes of being tortured for information, he's rescued by Castiel... Who is then mind-controlled by Naomi into killing him.
Way back from Season 1 there are two examples: Missouri Mosely from "Home" and Cassie Robinson from "Route 666", who never appeared again after their episodes. Missouri's role as psychic was taken over by Pamela, even though she was an interesting character with some history with the Winchesters, and despite Cassie being possibly the only woman Dean was shown to ever love and the fact that he told her he would come back for her, when it came time for Dean to return to a former love interest Lisa was used instead. This is not helped by the fact that they were both black and their replacements were white, given Supernatural's general issues with race and representation.
Due to the significant turnover rate of actors and actresses on the show, a lot of interesting and well-liked characters have either been killed off or disappeared into obscurity from whence they've never returned. The most notable examples have been Jackson Whittemore, Erica Reyes, Vernon Boyd, and Cora Hale, all of whom were central pack members with intriguing backstories, Ensemble Darkhorse status, and great importance to the plot that were never fully or even partially explored. It doesn't help that all of them were done away with in the same season, which effectively decimated over half of the original pack and has led many viewers and fans to consider everything after Season 3A to be Jumping the Shark or Seasonal Rot.
Several others could count as well, including some of the villains (Kali, Jennifer, the Alpha Pack as a whole) or secondary characters (Danny, the parents, Dr. Deaton, the Hales) whose colorful backstories haven't been expanded upon either due to death or literary neglect. With the removal of each central pack member above, a Suspiciously Similar Substitute has been introduced within a few episodes, taking further attention away from already established side-characters like Ms. McCall, Sheriff Stilinski, and Danny Mahealani.
War of the Worlds: The eponymous "Angel of Death" from the episode of the same name in this 80's series. The Blackwood Project (a group of researchers and a military colonel who are fighting extraterrestrial invaders looking to conquer Earth) find out that there's a rogue assassin running around the city, interrogating and killing scores of aliens. The Blackwood team learn that this assassin (an android from another world) wants to help them save Earth, and eventually leads the team in a battle royale with a horde of invaders (during which she demonstrates that she has the ability to bring people back from death). Then, she just up and decides to go back to her homeworld for reinforcements, and is never seen again for the rest of the series.
In the WWE, Muhammad Hassan was original portrayed as an Arab-American suffering from racism in a post-9/11 world. Judging by his character alone, he had the potential of becoming one of the biggest woobies ever. However, he was treated as a typical Foreign Wrestling Heel by the fans despite being billed from Detroit, Michigan to the point where he eventually became the very thing he was stereotyped as.
Paul Burchill's pirate gimmick, in which the wrestler discovered one of his distant ancestors was a pirate so he began to model himself as one, swinging onto the ramp from a rope and brandishing a cutlass, was much beloved by the fans. It even came about at the height of the popularity of Pirates of the Caribbean. But, the gimmick was axed prematurely because Vince McMahon couldn't understand why a pirate would be a Face.
Hade Vansen, a mysterious British wrestler who was supposed to feud with the Undertaker, was released before he debuted. Most fans feel it was a waste
When Dustin Rhodes] returned to WCW in 1999, it was originally supposed to be in the guise of "Seven," a ghoulish, pail-skinned character in a long coat and wide-brimmed hat. One vignette for the character features him staring at a child through the child's bedroom window, and then the child's eyes turn into empty black pits. When the character actually debuted, he floated to the ring (with assistance from some wires) and then Rhodes broke character and cut a worked shoot promo verbally bashing this gimmick, as well as the Goldust gimmick. The next time he was seen, he had a completely different gimmick, and the Seven character never even wrestled a match. The gimmick was actually the brainchild of Rhodes and his father Dusty, but the character was dropped after the network executives feared that he would be misinterpreted as a child abductor.
Dark Hunter Ancient. He's a unique case: started out as a decent character (evil but not outright malicious, and a founding member of the Dark Hunters), but was overall plain and unimportant. Not many would've missed him. Then, with no foreshadowing, he's revealed to be a Double Agent for the good guys. He's become interesting! He is then abruptly killed off and forgotten completely, rendering this reveal pointless (because no other character found out). Worse, the plot which led him to be killed was abandoned after that chapter.
Some might think they wasted Tren Krom too. Sure, he had a great impact on the story already, and was an interestingly developed character (some sort of a benevolent but still mean-spirited Eldritch Abomination who's terrified to see what the world he was once appointed to rule had come to), but he was bound to his island prison, which limited his use greatly. Then, he became free, and when we next see him... his pieces are all over the scenery. Justified in that killing off powerful characters was the point of this story, but still. There was great potential in the guy.
Telluris. A crazed and evil Gadgeteer Genius who does have a good side, but this is usually overshadowed by his mighty mechanical scorpion-war machine, the Skopio XV-1. The Skopio only ever appeared in one scene (not counting its animation model appearing in The Legend Reborn), in a difficult-to-get side story, and got trashed. Thus, the most defining aspect of Telluris' character was gone. Telluris also received an in-depth history, and even seemed like an actual likable character, only to be killed off later for no reason whatsoever, before he could do anything that had an impact on the plot.
Alternate-Teridax, the benevolent Alternate Universe-self of the story's Big Bad. He is brought to the main universe, but only appears for a short action scene where he brutally demolishes some Mooks, and is then forgotten. He doesn't even play a part in defeating the original Teridax, and nobody seems to care that he's there.
Miranda Lawson's demotion to extra in Mass Effect 3, despite being one of the main characters in the second game. Many fans lamented that since she was now on Cerberus' hitlist and wanted to track down her kidnapped sister, why on Earth would she turn down the chance to rejoin the Normandy, since with Commander Shepard and the Shadow Broker onboard, this would only have helped her achieve her goals?
Kelly Chambers qualifies as enough of a love interest in 3 that she triggers a Paramour achievement, and Shepard gets a photo of her to display in his/her quarters. However, she lacks any presence at all in the Citadel DLC to expand upon this. Nor does Shepard think of her during the ending.
Despite being the Big Bad of the second game and leader of the Reapers, Harbinger only appeared briefly at the end of Mass Effect 3 with one line.
Darth Nihilus in Knights of the Old Republic II: The Sith Lords is a mysterious Humanoid Abomination who communicates exclusively in the untranslated language used by Atris' Sith Holocrons, can destroy planets using the power of the Force and was featured very prominently on the cover of the game. Judging from cut content he is also substantially more powerful than undead Implacable Man Darth Sion. However, when you confront him he's easily beaten and turns out to have been a pawn of Kreia/Darth Traya all along and he isn't even named in the game. He gives the impression of being Too Powerful to Live more than anything. The real problem with Nihilus was more tied to the cut content of the game and because much of his character is fleshed out through two characters it is entirely possible to kill instead of conversing with. He isn't really that easy to kill either - again, the player has to interrogate characters and read between the lines to see that the Jedi Exile was the only one Nihilus couldn't devour.
Cheria in Tales of Graces had much much more room to develop, yet she seems almost put in there just to be the Token Love Interest. Kind of sad though; she's kind of a Woobie. Namco Bandai does seem to have realized this, as Cheria becomes more developed in Tales of Graces f. Still not nearly as much as she should be though.
Cheria was lucky compared to many of Tales of Destiny 2 characters. Most of the story focuses so much on Kyle and Reala that there's only a handful scenes for other members, especially so for Loni Dunamis (Kyle's best bud) and Nanaly Fletch (Loni's would-be girlfriend) who, after joining, seemed to exist only to 'tag along'. At least Judas and Harold got things to do in the past arc, what with the first being Leon Magnus Back from the Dead, the other is a historical person. And once the past arc is done, it's back to Kyle-Reala getting most focus again, and they're just 'tagging along'.
Yeager from Tales of Vesperia doesn't get a lot of light shed on his motives, despite being a main villain. What little we find out is pieced together through sidequests, and still leaves a lot unsaid.
Noishe in Tales of Symphonia is Lloyd's dog-like companion that, by the end of the game, is revealed to be a Protozoan, the first living beings to exist on the planet, and which take many forms throughout their extremely long lifetimes. Of course, other than a handful of times in the beginning, he rarely appears in cutscenes, even though he's tagging along for the whole game, and is used mainly as a way to avoid random battles on the world map until you get the Rheiards. By the time you see the cutscene explaining his origins, you'll probably have forgotten that he even existed.
The Shadow Triad from Pokémon Black and White are introduced as the most loyal servants of Team Plasma's boss. They have cool teleporting powers unlike anything seen in a Pokémon villain before. They are introduced really late into the game, are never fought and their only purpose seems to be passing down messages and items from their boss. In other words, any regular grunt could have filled in their role without any effort whatsoever. Fortunately, they had an expended role in the sequels.
Hammer from the CastlevaniaSorrow games, big time. As a former military member who provides a lot of the games' humor, he sure doesn't get a lot of attention, made worse by the fact that he was Dummied Out of Dawn of Sorrow from the extra Julius Mode as well as not appearing in Harmony of Despair when voice clips indicated that he was planned. Worse still, according to this interview, Iga also likes the character.
The majority of Touhou characters (and there are a lot) still manage to be interesting despite their brief appearance, and even ones with multiple appearances have large chunks of their personality and past underutilised or just unexplored. Fortunately the fighting Gaiden Games, Expanded Universe manga and Universe Compendiums take the opportunity to expand upon the characters in more detail and attention, but some benefit more than others; for example there is lots of info on the Scarlet Mansion residents but next to nothing about the denizens of the Underground, despite the numerous stories than can come from youkai facing Fantastic Racism from their brethren.
Chrono Cross suffers from this. A good quarter of the playable cast is closely tied to the plot and has absolutely fantastic storytelling potential, including one that was originally intended to be a returning character fromthe previous game and another intended to be the son of two chracters from the same. Other characters have interesting and engaging introductions that could've gone somewhere. But, to cram in the thirty-odd other cast members - including one-note and frankly ridiculous designs like the talking dog or sentient turnip - any connections to the previous game were dropped and characterization abbreviated. The end result is that barely anyone receives any character development past their introductions or, if they're lucky, a brief sidequest to unlock their Level 7 Tech. Then, with the exception of the male and female protagonists, they effectively cease to exist.
Renault in the 7th game. He has one of the most deep and complex backstories in the entire series... but he joins right before the final chapter, meaning it'll take about 10 playthroughs for you to actually realise this.
In the same game, Florina and Saindo interact once or twice throughout the gamenote by virtue of both appearing in the tutorial and remaining with Lyn at its end, as no characters under the player's control die when defeated until the Time Skip but generally not for anything more than a gag. What's particularly wasteful about it is that you have a perfect relationship to base Support Conversations on (where the meat of the game's characterisations occur with non-Lord units), and yet it doesn't ever happen.
Dead to Rights has several characters die after appearing in just a few chapters (if they're lucky), but the clearest example of this trope is Patch, a suave assassin who is introduced in a cutscene getting the drop on Jack Slate, killing the villain he was chasing for most of the chapter, and framing Jack for his murder, leading to the prison level. Making the scene memorable is that he has a distinct design from the other villains (dyed hair, the eponymous eyepatch, and a gold Luger), speaks with a subtle accent (unlike some other characters), and treats his hits as if he were an artist, complete with discussing his hit on the phone as if negotiating an art commission. He does not get a single line for the rest of the game, and does not appear again until four chapters later, where he dies anticlimactically in a Car Chase boss fight.
Sarah from Lost Odyssey seems to be the one party member who has little to no character development in the game. Her purpose seems to be to look after the kids and give Kaim an opportunity to show his softer side. She's also the only immortal who doesn't have an entry in the 1000 Years Of Dreams.
Adam from the first Shining Force is the token robot in a mostly fantasy setting. He is introduced alongside Chaos, who was his ally until Darksol reprogrammed him. The main problem with Adam: he's dangerously underleveled for how late in the game he joins (within the last seven battles). Even with a Power Ring, he's lucky to even scratch the softer enemies for more than one hit point of damage, and God forbid the enemy AI ever targets him in his currently fragile state. While he can be one of the best tanks with enough training, even people who like him find him to be a waste of time to bother training.
Prototype inflicted this to its own main character, of all people, in its second opus. Alex Mercer was fairly popular with fans of the first (though others did find him unlikeable); his look and backstory were fairly unique, he was recognized as Bad Ass, and he got a bit of character development throughout the game, going from Villain Protagonist to on his way to become an Anti-Hero. Yet, Prototype 2 has him turning evil for unclear reasons and ending up killed by the new main character, with few character traits being carried from the end of Prototype to his behavior in 2. To put it worst, he has a reduced role even as a villain, and his rivalry with new protagonist James Heller isn't explored. Many believe it was because of this decision that caused the game to not sell as well and led to the near bankruptcy of Radical.
Word of God is that their aim with Danganronpa was to create a game where the entire cast is a fully fleshed out character and has some impact on the plot. Dangan Ronpa is also a murder mystery game in which those same characters are being pushed towards the Despair Event Horizon by a sadistically evil mascot and pressured to kill each other to escape. One of the biggest examples in the first game is Ishimaru, who, after the death of Oowada, suffers a Heroic BSOD and only manages to snap out of it by going completely insane and Hot-Blooded to the Nth degree. He's then then killed soon after, before anything can be done with this.
Princess Daisy. She's a friend to Peach, the love interest of Luigi, and is at a sharp contrast to many of the other female characters yet she's destined to only appear in party spinoffs. She even has an entire kingdom, Sarasaland, to explore.
Bowser in Paper Mario: Sticker Star. After being a hilarious villain in Paper Mario 64, starring his own playable sections in Paper Mario: The Thousand-Year Door and being one of the four protagonists in Super Paper Mario, he's virtually Demoted to Extra, appearing just in three scenes (one of them, admittedly, is the final battle, but still) and having a whooping amount of 0 lines in the entire game. It's especially painful since this is the series where Bowser has pretty much acquired his entire lovable yet evil personality, instead of the mindless brute he is still portrayed as in the platformers.
Final Fantasy Tactics is a particularly glaring offender. Because any party member can die permanently in combat, the designers didn't bother to write any further material for characters once they join the party permanently. It gets to the point where it's almost disappointing to get a new party member, because it means that the character in question has been reduced to a block of combat statistics and will never do anything interesting in-story again. This is especially galling with characters like Agrias and Mustadio, who join early in the game and would likely have gotten a lot of development in any other RPG, or who like Meliadoul (whose father is the Big Bad for much of the game) still have an obvious connection to events in the main plotline.
There are very few times where the optional characters contribute anything to the game after joining. Mustadio is needed to recruit Construct 8, Cloud, and to get Reis' human form. In the PSP version, you need Mustadio and Agrias to get a super-powerful accesory. The PSP version also adds an optional sidequest for Beowulf and Reis. This is a complete list, leaving the other characters pointless to the story.
Yuffie from Final Fantasy VII could be considered this by some. She is the princess of a nation that was invaded and defeated by Shinra. This same nation is again hit by Geostigma, essentially The Black Plague of the VII universe and yet little is said about how it's handling this. It is said that this country was once great and mysterious, and yet Square decided to expand on Cloud's story and make a game centered around Vincent Valentine rather then explore a country with it's own history and culture that is vastly different from the one already shown in series. Given what history has already given us, Square could've used some real world examples and made a story centered around politics and Yuffie's history growing up in a vastly different setting then Cloud and the rest of the cast. At least we get to see her in Kingdom Hearts.
Sonic Generations included relatively few of the Classic characters: Sonic, Metal Sonic, Tails, and Eggman. It didn't include Classic Knuckles or Amy, even though they were prominent characters before the Modern Art Shift.
The Deadly Six from Sonic Lost World are huge examples of this. They could've made very interesting and memorable villains, and while their character interaction is great, despite their cliche personalities, everything else is wasted. We know next to nothing about them, why they became the Deadly Six, where they came from, why they were sealed away, why the conch controls them, or what a Zeti even is! Not to mention their fate was VERY anticlimactic and ambiguous. Most we get is some vague little snippets of their relationship to each other and that's about it.
Advance Wars: Days of Ruin has two. First is Isabella, who is a fully playable CO in VS mode but is never used once in the campaign mode and has a very minor role on the story, only existing to be Will's love interest and to drop a bit of exposition. The second is The Beast, who is the primary antagonist for about half the game AND has his own unique battle theme, design, etc, but is completely unplayable. Pretty much everyone would have rather seen The Beast selectable in VS mode instead of Isabella.
In Disney Princess Enchanted Journey, Zara is an interesting character with a vaguely defined backstory and an implied history with the heroine, has a cool design, and has the distinction of being Disney's first wicked princess. She only appears at the final boss fight, and is never mentioned before or after it.
Pretty much any character from Resident Evil that isn't Chris, Jill, or Leon has completely gone to waste, but special mention goes to Barry Burton. He's quite popular outside of Japan and absolutely loved by Americans because his cheesy lines, overacting, love of huge guns, and his portrayal as a loving family man make him akin to an action star from the 80's, but has vanished completely into the pit of Plot Holes along with a lot of other characters.
Kid Icarus: Uprising has Magnus, with a cool design and backstory, with a very fitting voice actor. He appears in a grand total of three chapters.
The first game suffers from this in two ways. First, the game treats all party members as expendable, and thus doesn't feel the need to flesh any of them out very much, leaving characters having to endear themselves to the player through sheer force of personality (like Minsc and Xan) despite some promising character ideas (like Kivan.) Second, many characters are only encountered well into the game, when the player will have already gathered a dedicated party and won't have room to recruit them. Hell, a few characters are only encountered when the titular Baldur's gate becomes accessible in Chapter 5 (out of 7.)
Imoen is ntroduced as the player's plucky childhood friend/half-sister, she was added in at the last second when playtesting revealed the beginning of the game to be too difficult to go alone without recruiting two nearby evil-aligned characters, and thus she doesn't even get the minimal amount of inter-party banter that the first game had. Fortunately, the sequels more than made up for her lack of presence in the first game.
Many recruitable characters from the first game are flat-out killed with little fanfare in the second game (like Ajantis, Xzar, Montaron and Safana,) ruining any chance at developing them altogether, and fan-favorite Xan is relegated to the tutorial section where he doesn't even get to show off his character quirks. Fortunately, there are mods that fix this.
No More Heroes 2: Desperate Struggle seems to do this deliberately with Henry to tease the fans. After the revelation that Henry will be a playable character, the player soon finds out that he's actually only playable for one single boss fight (that's a Giant Space Flea from Nowhere), and outside of that only makes an appearance in a few scenes, where he takes out three of the ranked assassins off-screen before calling Travis and showing brief glimpses of fights that could've been.
The ranked assassins, in both games. Nearby every ranked fight is memorable in some way, and a few of the assassins could even potentially carry more of the game (like Kimmy Howell or Bad Girl,) but other than Shinobu, and Letz Shake and Destroyman getting rematches in the second game, none of them ever appear outside of their boss fights.
The Count of Groundsoaking Blood from Boktai is easily the most fascinating and well-developed of all the villains. He's the one who killed Django's father, the proxy reason Django himself gained his vampiric powers (as well as reawakens them in the third game), forms an Enemy Mine scenario with Django in the third game (Sort of, it's complicated), and has a completely under developed romance with Queen Hel. Unfortunately he's the first level boss in every game he appears in, and thus always dies before the plot of the game even kicks off.
The "To Thine Own Self" arc of General Protection Fault introduced some side characters who would have been interesting in their own right as counterparts to the main cast, but got killed off before long. Examples include a version of Yoshi who is a savant at engineering but otherwise mentally retarded, Wong Li, a diminutive yet extremely powerful operative and a Shrinking Violet version of Sharon. Unfortunately, most of the resistance characters are implied to have been killed off when the resistance hideout is raided, and Nega-Sharon is a Reverse Mole for the Emperor, and gets killed when an explosion causes the roof to collapse on her.
Homestuck: The trolls of Hivebent hover somewhere around 'deuteragonist' level, but are still this. (They're introduced in Act 5, most of them are dead by Act 6, and they're the protagonists of a compelling, highly abridged Story Within a Story that Hivebent gives us only an idea of.) They each have their own distinct personalities and methods of coping with the Fantastic Caste System and their species' truly messed up culture. They have an alien system of romance that the author created specifically to bait shippers with. It should come as no surprise that they're also Ensemble Darkhorses par excellence.
Presumably; this was what the producer thought about Kristen and Roscoe. Before he canceled the original Sims Big Brother 7, the two were brought back as the guest star players. Both were evicted second and didn't have a chance to develop (That and SRN admits that he had almost no creativity while working on Sims Big Brother 4 anyways; and it shows.) However when the viewers chose the cast of All stars, Roscoe sadly didn't make the cut (He did have several amusing moments; though, more than can be said for Kristen) but Kristen was one of two people from season 4 that made it in - the other was Johnny. Kristen wasn't even a producer's choice!
Unfortunately; the same could be said about a lot of the big brother 4 cast. CJ seemed almost a background prop despite being popular enough to win (Viewers voted on the winner) Brian and Sam seemed to be in control of the game, heck, Sam is the only player who was never nominated.
The viewers also thought this about Dana, too. Dana was another early boot from Big Brother season 2 but was voted in as well.
So, so, so many of the background villains from The Tick. They all had hilariously over-the-top cartoonish appearances, abilities, and quirks, but most of them didn't even get named let alone to do anything else.
Kim Possible: Adrena Lynn would have been a great villain, but she was only a one-shot villain because she wasn't as popular as the other recurring villains.
One episode had a cross dressing character known as Carolyn/Jamie. In the episode he became close friends with Peggy, and as Jamie even got along well with Hank and the rest of the gang. After he taught Peggy about how it's okay to be different he was never seen again to the dismay of many fans.
Bobby's girlfriend Debby, introduced at the end of "I'm With Cupid", after Bobby had finally gotten over Connie he meets her and finds out they share a similar sense of humor and introduces her to his parents who approve. The ending implies we will see more of her in future episodes but she is never seen or mentioned again.
Winx Club: Chimera. Her introduction showed quite some promise, but then she got saddled with a Guess Who I'm Marrying? plot, which went in a completely predictable direction... that is, except for a couple things that viewers totally expected to happen: the plot taking a trip to her school, Stella having to make a truce with her, and Stella having a decent final battle with her.
Rocket Power introduced a potential love interest for Reggie, in an ep that shows her being afraid to show her real sports skills. Total episode count? Two, with his only other episode centering around Reggie feeling offended that she wasn't invited to play rugby like her fellow friends. At least with Breezy (who was similarly introduced for Reggie's dad and got the same episode count), she had the excuse of being a traveling saleswoman...
Remember that Trixie Tang is actually a tomboy scared of alienating her 'friends' if she behaved anyway that she wasn't expected to? And even before that, in her first appearance, she showed that she was nice deep down, rather than just a spoiled Jerkass? The writers sure don't...
Ms. Sunshine AKA Ms. Doombringer, ironic since in her only episode she vowed to Timmy that she will return someday, but as Crocker said "But not someday soon.".
Ezekiel's was the first contestant voted off in season one and was left out of season two, but got quite a sizable fan base anyway, perhaps especially due to the extremely popular Total Drama Comeback Series. There was a whole mini-mystery about whether or not he would be in season three, and when it turned out he was, fans got really excited... and then he got voted off first again. And then, just so his fans really understood how much the show's writers hated them, he devolved into an expy of Gollum for no logical reason, and got to "come back" as a Running Gag before falling into a volcano in the finale. Needless to say, many of his fans have been crying this trope.
Eva hasn't had much screen time either. She may not be the best character, but she deserves more screen time. (Ezekiel has been in the competition more than her. EZEKIEL!) A good example of how Eva's character was wasted was through the World Tour Aftermaths. After appearing as the angry reporter in the first Aftermath, she quickly became Out of Focus as the show focused on the feud between Bridgette/Geoff and Blaineley.
As with Eva, Katie and Sadie haven't received any attention since Island. Heck, it's safe to assume that out of all the original campers, they've been involved the least in the competition, with Katie going on the longest without ever competing (even Eva was given a chance to come back.) They're easily not the most well-rounded out of the cast, but they could have been. Katie and Sadie's personalities revolve entirely around each other, which gives them a lot of room to develop as their own person if they were ever separated, and that could have lead to hilarious scenarious. In fact, they were separated for a time in Island when Katie was eliminated. What did Sadie do without her? Absolutely nothing. You could count the number of times she spoke since that episode up until her elimination on one hand, and the only other camper she had onscreen interaction with was Lindsay. Since then they have been reduced to the Peanut Gallery in both Action and World Tour, because the writers apparently do not know what else to do.
Kevin was generally liked by the fandom, mostly as a love interest for Meg. He was hardly ever seen, though—and then suddenly, out of nowhere, his father casually mentions that he died in Iraq. As far the fans knew, he hadn't even been in Iraq. It was retconned that he wasn't really dead after all, and Joe's casual mention of his "death" was actually because the army did a paper work mix-up and Kevin had faked his death to avoid having to be in the army.
Meg is an odd example: she's a major character who appears in just about every episode, but Word of God admits they have no idea what to do with a teenage girl character. Their solution is just to show her being hated by everyone for no reason, mocked for being fat and ugly, and slowly slipping into depression/insanity. Jeez.
Maybe the ultimate example would be Vinny, the new Replacement Goldfish dog the Griffins adopted after Brian's sudden death. The event bringing him onto the show was erased from history with only one episode between that and his introduction.
Every minor kid has his own fandom, even though many of them are only meant to be one-off characters. The show has a good number of A Day in the Limelight episodes, but unfortunately, we all just have to accept that Damien isn't coming back anytime soon (outside of background cameos as an animator's joke).
Gary Harrison the Mormon kid was fairly popular during his debut and seemed like he would become a recurring character, but alas he never appeared again aside from a brief non-speaking cameo.
The new characters from The Movie such as The Mole, Gregory and Dr. Vosknocker never appeared again (outside of a very brief cameo from the Mole).
Although hated by certain factions of the fandom, there are also those who regret that Rebecca and Mark Cotswolds didn't become semi-recurring characters, as the fish-out-of-water dynamic appealed to them. While Mark managed to get non-speaking cameos for a few seasons afterward, Rebecca was never seen again. Kenny's one-time girlfriend Kelly (also either loved or hated depending on the fans) is another case of a character that the fans more likely remember than the creators would.
13-year old Princess Bubblegum in "Too Young". She has only a little over an episode before being changed back to normal, and that aspect of her is never brought up or mentioned ever again.
Marceline sometimes goes half a season without appearing at all, and even in her A Day in the Limelight episodes she still gets shafted for screentime. The worst example is definitely "They Went to the Nightosphere"/"Daddy's Little Monster", a two-part episode set in Marceline's original home and appears to focus on the issues between Marceline and her father... only for the vast majority of the episode being Finn and Jake's wacky adventures with demons and her father getting more screentime than her, with Marceline barely appearing.
Lady and Jake's children. Five characters with varying combinations of their parents magical abilities, but only two of them have gotten any lines (in english, at least), and only one of those received any actual development. Despite their significance, they've all been relegated to background characters.
Flame Princess has a lot of potential as a character, especially as her continual wavering between good and evil meant she could work equally well as a hero or a villain, but was mostly relegated to just "Finn's girlfriend" and most of her development revolved around him. "Frost & Fire" gave her more agency and "Earth & Water" had her usurp her father as Flame King, hopefully signifying her rise to prominence. But her only episode since then, "The Red Throne", has her rendered powerless, forced to rely on Finn and Cinnamon Bun, and even her father and his co-conspirator got more lines and screentime than her.
Blight is the biggest offender. He was the Big Bad of the first season and set up as the Big Bad of the series period, but he never returned after the first season's finale. He did get to appear in the comics, though.
Most of Terry's supporting cast was sorely underused, most prominently his mother Mary, followed by his brother Matt and his girlfriend Dana. For all that they tried to make Terry different from Bruce, they neglected the characters in Terry's life that Bruce could never have had.
Melanie, a girl who was once a member of the Royal Flush Gang that Terry had a mutual interest in only appeared in three episodes. She had a character arc in those few appearances, but many fans wanted to see more of her.
Bane gets used for one episode, and the next time Batman has to face a huge muscular villain capable of breaking his back, it ends up being Joker using Bane's venom. He then showed up in a few other episodes with no lines, and being now able to be brought down easily.
While not really badly used, Poison Ivy showed a lot more potential that was realized in the spin-off comic series far more than it ever was in the show.
Bunnie Rabbot made interesting use of the show's robotocization concept and had kickass cyborg powers to boot. However she had a supporting role in the majority of the first season and was Demoted to Extra in the second, arguably getting the least amount of development time out of the rest of the Freedom Fighters (keeping in mind Rotor and Tails were also heavily Out of Focus for most of the show's later run). The comics adapted from the show utilize her a bit more, but still play her as one of the more minor leads.
Tails. They took Sonic's best friend and sidekick from the games and reduced him to a minor character. He stays home most of the time, resulting in him hardly ever participating in any of the missions. When he does, his contributions are little at best or pretty much nothing at worst. A later season two episode tried to fix this, but by that point the show was almost over. Word of God said he would have been more important in the third season, but that still doesn't explain why it took so long to give a major character from the games a notable role.
General Immortus from the fifth season. He's one of the core members of the Quirky Miniboss Squad and he's a military genius with millennia of experience, but at the end of the day he appears in only a handful of episodes, in only one of which he has lines, and does little but boss the mooks around. In the Final Battle, he gets an ignominious curbstomp where his three companions all go down fighting hard (or at least the Brain has a Dragon fight hard and leaves a booby-trap himself).
Jinx and Kid Flash, though less the characters and more the dynamic between the two. They get ONE episode devoted to them, and then vanish until the finale where Jinx arrives with Kid Flash and proceeds to fight alongside the Titans. Bet that was interesting character development...
Koh the Face-Stealer, a fascinatingly creepy spirit who looks like a giant centipede and can steal the faces of victims to wear as his own. With tantalizing hints that he has dealt with the Avatar in the past and will do so again in the future, he never reappeared in the show again.
For some, Fire Lord Azulon who only got one flashback scene in one episode. He apparently was a firebending prodigy like Azula and was a feared general before becoming Fire Lord.
Also Lo and Li, Azula's ancient instructors. Nothing is revealed about them other that they apparently aren't firebenders despite instructing Azula on her firebending.
Luna's villain persona Nightmare Moon had everything a villain needed: a cool design, a clear motive, and even henchmen. Unfortunately, bringing her back would completely undo the Character Development that Luna has since gone through. Season 4 got around this problem by featuring a return from Nightmare Moon... in the form of a flashback Twilight gets of the night she was banished to the moon.
King Sombra, out of all the main antagonists, if not every single antagonist in the show,(or even every character period) is the only one who has had no opportunity to experience any character focus, despite being highly competent and frighteningly dangerous. With little interaction with the mane cast, barely any dialogue, very little screen time and being Killed Off for Real, he was written as more of a mindless beast than an actual villain. There was evidence to suggest he was going to be the show's first recurring villain, until the official comic used Queen Chrysalis to fill that position.
Celestia, although she appears in numerous episodes, never receives any character focus like Luna and exists mostly to provide exposition. What hints do exist as to her past and personality - especially the ones that might indicate she's The Woman Wearing the Queenly Mask - are tantalising enough to make her a prime target for fanfiction writers, but they're only hints and near nothing is really known about her.
Queen Chrysalis spent the vast majority of her screentime impersonating Cadence, even during her Villain Song, so her true from is only seen for about ten minutes and leaves no opportunity to explore her motives or personality, or even what changelings actually are. She gets a much bigger role in the IDW comics, however although they're official they are not from the same writers as the show and it's doubtful they're part of regular continuity.
Only two episodes ("The Bus Boy" and "Cracked") featured a pair of alpha-bitches who tormented Dexter.
Douglas, who only appeared in a handful of episodes. He could of been a cool non-Deedee companion to Dexter, but he sadly never evolved beyond a Satellite Character. Made no better that the Tartakovsky-less episodes changed his name to Mordecai.
Olga/Lalavava, Mandark's little sister. She appeared once and was never seen since. Made even more bizarre because the end of her episode pretty much confirmed that we'd be seeing more of her.
A 12 year old Opposite-Sex Clone of the title character, Danielle "Dani" Phantom. While there are some fans who regard her as The Scrappy, others see her as wasted potential and could have had an arc and a greater role. It is rumored that if the season 3 lasted longer, Danielle was going to be discovered by Danny's family and accept her and she'd become Danny's little sister instead of posing as his cousin living on the streets. Also considering that in the episode she debuted in, Sam and Tucker admit they're tired of being Danny's sidekicks (even confirming in Season 3 they don't call themselves that anymore) and in comes a younger, inexperienced ghost hybrid that could have become Danny's new sidekick. Such a route could have developed Danny as an older brother and a mentor to a younger halfa.
Freakshow, the evil ringmaster of Circus Gothica, could have become a cool re-occurring villain in the series. First of all, he was the only human in the series to be an actual villain (Any other human that opposed Danny was either the half-ghost archenemy Vlad or amoral ghost hunters who viewed all ghosts as Chaotic Evil). Second, he used magical items as opposed to technology. Third, he and Jazz both shared "Ghost Envy", giving them a Not So Different vibe. However, he's only the main villain in the season one finale and the Big Bad in the 3rd TV movie. That was it.
Transformers Animated: Team Athenia and Team Chaar were hyped up considerably for the delayed season 3, both were teams brimming with old characters re-imagined. They got magazine profiles, and focus in the trailer. The three part season premiere opens with their battle... and they never appear again outside of cameos.
While Batman: The Brave and the Bold was meant to focus on lesser known heroes and villains of the DC Universe, Batman's rogues gallery, with the exceptions of Joker, Catwoman and Ra's Al Ghul, never played a real part outside of just appearing to let us know they exist in this show. One example is Poison Ivy, who only played the role of the villain in the opening of one episode where she takes over Gotham and considers sparing Batman if he agrees to marry her.
Several new characters are introduced only to be seemingly forgotten and thrown aside so the more major players could get attention. Rocket was a late addition to season 1, but barely got to be seen with the team before the timeskip, which had she and Zatanna promoted to the Justice League and barely around. The Tim Drake version of Robin was also underused in Invasion, barely getting much characterization despite the potential of his introduction. Wonder Girl had similar lack of development, which led to fans being confused when she decided to date Robin in the series finale.
Tula/Aquagirl and Marie Logan each appeared in one episode in Season One before being revealed to have died during the Time Skip prior to Invasion.
The entire Injustice League. Despite a lineup featuring the original supervillain, a guy with all Captain Marvel's powers, a guy with all Doctor Fate's powers, and The Joker, they appear in all of one episode, lose, and with the exception of Count Vertigo and a later cameo by Wotan, never show up again. Most of them wouldn't be out of place in the Light's leadership, but nonetheless, most of them don't even get lines, with most of their dialogue going to the Joker.
Aladdin: The Series has the Reality Warper Chaos, who has more magic in his whisker than a palace full of genies, where Mirage even fears him, and possibly one of the most powerful characters in the Aladdin universe, if not the entire Disney universe. Appeared only in one episode.
The Simpsons has a lot of one-shot characters that are quite popular because of their role and/or personality and could have had many more stories about them, such as Jessica Lovejoy, Allison Taylor, Alex Whitney, Colin, and pretty much every guest spot child character.
Hank Scorpio is an Affably EvilBond villain parody with some of the best lines in the series' history, and one of the few people who is genuinely nice and supportive to Homer. Unfortunately someone trying to Take Over the World doesn't work so well in The Simpsons, and he's never been mentioned again. (Though his popularity did mean the villain of The Simpsons Movie was a blatant Expy of him, complete with the same voice actor.)
Samantha Stanky could have been a Love Interest for Milhouse (and end Milhouse's embarrassing attempts to win Lisa over) and a second best friend for Bart. Sadly, Samantha's prudish father sent her to an all-girl convent school, where she is locked away from the outside world, and hasn't been seen or referenced since.
Herb Powell, Homer's long-lost half-brother, only appeared in two episodes and was never heard from again after regaining his wealth and reconciling with Homer. Given the huge amount of stories that have come from the Simpson's extended family this is disappointing.
Mr. Bergstrom was an excellent contrast to the rest of Springfield's teachers, who actually cared about his students' education and got them interested in school. Him being a possible mentor to Lisa alone had potential, but he only appeared in one episode.
The sixth season of the 2003 incarnation of the Teenage Mutant Ninja Turtles may not be the most well liked season of that show, but one thing that viewers did like was the introduction of the Dark Turtles. Four altered clones of the turtles combined with alien DNA, each bred specifically to fight their counterparts. In their final appearance of that season, it was shown that the four weren't complete evil, as Leonardo's clone showed signs of a conscience during a time he tricked them into letting him stay with them and at the end started to treat his brothers with a bit more respect. Due to that season's abrupt ending, and only one character introduced from that season, who wasn't any of the clones, having remained in the cast, the Dark Turtles and their arc were never seen again.
The 1980's series introduced a female reptilian mutant named Mona Lisa as a love interest for Raphael. She has her share of fans, but Eastman and Laird aren't among them, so she was never seen again after her debut episode. At least she got her own action figure.
Ever since his introduction, Thomas from Regular Show basically serves no purpose other than to be the Butt Monkey of the episode. We see sides of him being the Only Sane Man in situations, but is constantly shot down by the others.
Zordrak is an unusual case, in that he is the Big Bad and makes appearances in every episode. However, despite his menacing concept and characterization, nearly every episode had him order his minions, the Urpneys to do the schemes and usually having them with the role as central antagonists. While Zordrak was given odd moments of involvement in Season One (along with a chilling origin flashback), his role was completely diminished to a useless despot afterwards, almost always limited to a superfluous cameo each episode ranting at the Urpneys to think up a new plan to get the stone. He was granted a couple moments concocting plans in the final season, but by that time it was too little too late.
There are several alternate antagonists such as Zarag and Urpgor's Auntie. They made appearances only Once a Season, and even in those were secondary antagonists to the Urpneys, leaving little time for development.
Thomas the Tank Engine is profound at this due to it's Merchandise-Driven drive to introduce Loads and Loads of Characters. Almost every season introduces two or three new engines that get a spotlight episode each...and then are forgotten about, usually appearing in a handful of background cameos at best. This tends to be zigzagged in it's treatment of the cast from the original The Railway Series novels (Daisy appeared in only three episodes, compared to the books where she became a prominent character, however minor characters such as Bertie, Harold and Diesel are regulars in the show and have been granted numerous spotlight episodes).