Viktor's assistant Sky appears to be a somewhat important character, even appearing in Viktor's flashback. However, she is killed rather unceremoniously only to fuel Viktor's angst. Fans feel like she should have been developed as a character in her own right.
Tigerhawk in Beast Wars appears very late in the series, flexes some heavy-duty Merchandise-Driven power by blowing up the Predacon Base, indirectly causes the death of Tarantulus, and then is pretty unceremoniously destroyed only two episodes later by the Nemesis. He's barely even a character, getting about as much dialogue as Ivan Drago and mostly only serving as a Plot Device than anything. It was caused by Hasbro flip-flopping on whether or not to release his toy: at first they did so he was introduced, then they changed their mind and he was snuffed out, and then they decided to release the toy anyways.
Ben 10 had Alien X, introduced in Ben 10: Alien Force. As a character, him being a Story-Breaker Power due to being a Reality Warper meant he wasn't that useful as compared to other aliens who had flaws to even things out; the waste of character was that they'd made him too powerful and his powers not being dialled back so much and being a near-Invincible Hero was an unusual use of this trope, because while his species was given lore and characterization, the character was wasted for not being given enough flaws aside from the Split Personality and then Ben gaining 100% control over Alien X, rendering his personas Serena and Bellicus to go out of focus. Some of the fandom felt that he was wasted for being too over-the-top in mannerism and behavior, even with a glittery Humanoid Alien design.
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.
Darkwing Duck: A few of the villains like Lilliput or Bugmaster with interesting powers only made one or two appearances.
Buzz Lightyear of Star Command. Ty Parsec. For a guy who's been saved more than 50 times by Buzz (a lot of people theorise that this was an exaggeration which is why Ty is so bitter) and was then transformed into the Tragic Villain Wirewolf, and has a hilariously sarcastic and cynical personality, Ty shows up in a mere two episodes. He's 'cured' at the end of the second and is never seen or mentioned again.
DuckTales (1987) wasted three perfectly good characters — Launchpad's loving family; Ripcord, Birdie and Loopy McQuack are very well liked and fondly remembered despite only appearing once in the episode "Top Duck" (with Ripcord and Loopy getting a non-speaking cameo in "Til Nephews Do Us Part"). Fans requested they make another appearance but all they got was a cameo in the Darkwing Duck episode "U.F. Foe."
Ed, Edd n Eddy has Nazz, who has the distinction of being the only girl on the show who isn't depicted as being psychotic in some way and she's The Heart of the cul-de-sac all the boys (except Jimmy and Rolf) have a crush on. Unfortunately, throughout the show's run, very little is done with Nazz, she only has three episodes about her (Plank has more storylines) and until later seasons she was a relatively Flat Character. Later seasons turned her into a bit of a Dumb Blonde, but she remained quite unremarkable in a cast of wacky, memorable characters. The Movie seems to address this by giving Nazz a prominent subplot with Kevin, a last name (the only other character besides the Kankers to get one, in fact) and she Took a Level in Badass, but overall a lot more could have been done with her character besides being the Only Sane Man of the cul-de-sac kids.
Francine Bishop from "The Shreds Fell Like Snowflakes" only gets one appearance despite being a compelling Young Entrepreneur with her ice sculptures and acting as the loyal and protective sister of Vallejo's disgraced old partner. Additionally, she attempts to get revenge on Vallejo for not standing up for her brother, using an impressively complex plan that she refuses to abandon even after her brother tells her to let the grudge go. Many fans would have loved seeing her continue that feud in future episodes and/or make peace with Vallejo, but neither ever happens.
Robert Chestnut from “Links in a Chain of Honor”. He is the president of the Absurdly Powerful Student Council, an ex-safety patrol member, a secret Caring Gardener, and someone pressured to live up the legacy of his older brothers while also pressuring his younger brother (who he does have some affectionate moments with) the same way. He could have been a good semi-regular, but only appears in one episode as the culprit, with the series never even exploring the fallout of his actions and exposure.
The Ghost and Molly McGee: The Chairman is an intimidating Grim Reaper-like figure who created the Flow of Failed Phantoms and made the laws about ghosts spreading misery so that he could feed upon it. Fans assumed that he was being setup as the Big Bad to be confronted at the very end of the series, but he's easily dispatched by Molly at the end of the first season, before anything else can be revealed about him, and he never even says a single word.
Justice League: In the episode "Eclipsed," we meet a Glenn Beck-esque right-wing pundit by the name of Gordon Godfrey, who goes on ridiculous rants against the League for most of the episode (i.e. "Since they came around, half of all marriages end in divorce, and the other half end in death!"). In the original comics, "Gordon" is the human guise of Glorious Godfrey, Darkseid's Minister of Propaganda, yet Godfrey only appears in this one episode and shows no signs of being an Apokaliptian or indeed anything other than an ordinary, and annoying, human.
The Cheetah is Wonder Woman's Archenemy in the comics, so a lot of fans assumed she would get more character development after receiving a lot of focus in her debut episode. However, she got Demoted to Extra... although Word of God is that she was meant to beKilled Offscreen by Solomon Grundy in her debut two-parter, and was only saved by an animation error showing her alive later on, so getting to appear several times more was an unexpected boon for her.
Longshadow, a former Cadmus agent and the show's version of Apache Chief, is shown joining the Justice League in the end of his debut...and is never seen or heard from ever again. There isn't even any confirmation as to how long he lived or what he even accomplished during his time as a true hero.
Hal Jordan and Kyle Rayner only appear as cameos in the entire series, and have very little interaction with the League. One episode even teased at Hal switching out with John, only for it to be shot down as the Guardians call John out on trying to use it as an excuse to get a break from his messy love triangle. Heck, at least Kyle and Hal got cameos in the series, poor Guy Gardner doesn't even exist in the DCAU it seems!
Speaking of the Green Lanterns, Star Sapphire appears as a villain several times, but as for who she actually is (if she actually is Carol Ferris) or what her vendetta against the Green Lanterns is never explored.
Kim Possible: Many of the characters who only appeared in one episode have interesting backstories and abilities but sadly, didn't get much exploration:
Adrena Lynn would have been a great villain and a great Foil for Kim, both of them perform stunts but Kim does it for helping people and genuinely does her own stunts while Adrena does it for fame and a fraud who faked her stunts. So she was only a one-shot villain because she wasn't as popular as the other recurring villains.
Will Du from "Number One" was meant to be a recurring character in the series. He was set to be both a rival and potential love-interest for Kim, roles he still could have fit in the series proper; a trained operative who works alone versus a freelancer who works with her friends. Never appears again.
Prince or rather President Wally, could've served as the team's financier since he did tell them that he would meet them again.
Same with the Knights of Rodeghan. Would they still try to assassinate Wally despite his intentions of turning their country into a democracy?
The show could have done more with Kim's relationship with Josh and Ron's relationship with Tara and/or Zita (instead with Ron's former he wasn't even aware of Tara's crush, just like with Yori).
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. Though considering she and her mother turned Stella's own father against her...and nearly murdered him at one point...many fans would also feel that she was too far gone to be redeemed.
Mirta. While the show dropped her off the face of the earth after Season 3, and barely used her after Season 1, "Mirta joins the Winx" fanfictions are still popular, normally dropping Aisha for her.
Rocket Power introduced a potential love interest for Reggie, in an episode 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...
Ditto with Kevin C. Cucumber, who could have been a very good Evil Counterpart for SpongeBob if given the chance. However, he has only appeared in one episode. His child counterpart appears in Kamp Koral, albeit mostly as a Living Prop.
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.
Joyce Kinney was reduced to a Suspiciously Similar Substitute for Diane Simmons after just a few episodes despite showing potential as a possible antagonist.
Sanjay and Craig: The series really seems to love using this trope to some of its characters.
The best example of this would be Sam Lastnamè. She is so beloved by the show's tiny fandom, that she is prominently featured in a lot of fanworks as one of Sanjay's group of friends, as well as being Megan's best friend. Sadly, in the actual series, she only appears in about 7 episodes throughout Seasons 2 and 3. Only two episodes (Butts Up and G.U.T.S. Busters) have her in a major role, the rest of them only have her in background roles. It's gotten to the point where it is believed that she is the mascot of this trope.
Every minor kid has their 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.
Most of the aliens never have a major role (or even appear again) outside of the episode that introduces them. It happened to Najix the shapeshifter (better known as the ice cream-crapping taco) and the Joozians from "Cancelled", the Intergalactic Police from "Pinewood Derby" and the Gelgameks from "Red Hot Catholic Love". The latter especially could have been revived both for some topical satire against the Catholic Church and for the thought-provoking idea of aliens believing in God and Jesus, but it was not meant to be.
Season 20 has so many plotlines that in the end none of them gets really resolved, so we have characters that either do nothing (Bill and Hillary Clinton, Bill Cosby, JJ Abrams), are put in prison and more or less forgotten there (all of the trolls/cyberbullies) or start as an Overused Running Gag and suddenly become irrelevant (the Member Berries). On top of that it concludes with a Reset Button of sorts and the creators stated that they won't attempt a continuity-heavy season again, so it's likely that we won't see any of them again outside of some brief cameos.
Darth Chef from "The Return of Chef". Even though he is still at large by the end of the episode, he has yet to reappear beyond a brief cameo in the opening credits despite the plot potential that could come from the boys realizing he's still alive and potentially having to face off against a fully-brainwashed Chef. He could even serve as a possible means for Chef to return to the show proper (albeit with a different voice actor). Even when Chef briefly returns in South Park: The Stick of Truth, it's as a Nazi Zombie with Darth Chef not even being referenced.
Martin, Finn's father, an effective Hate Sink and Shadow Archetype to Finn with a mysterious backstory. We first meet him when he was in the Citadel for some kind of "Cosmic Crime," the likes of which include killing a god. Clearly this guy is Big Bad material, right? Not so much; he appears on and off during the sixth season, mostly just as a Jerk with a Heart of Jerk conman, before being Put on a Bus without any real backstory revealed, including what he did to wind up in the Citadel. We find out a bit more about him during the "Islands" miniseries, but even then there's a huge gap and it just opens up more Alternate Character Interpretation.
Rattleballs is a badass sword-fighting robot who was made by Princess Bubblegum, and narrowly escaped death at her hands. This connection to PB's colder side would make for great episodes, as would the fact that his introductory episode ends with him deciding to protect the Candy Kingdom from the shadows. But since his introduction, he's only been seen in a small handful of minor cameo appearances.
Orgalorg is the true form of Gunther, an Eldritch Abomination from outer space that has been around since before the Big Bang. The episode of his namesake sets him up as one of the most dangerous and powerful villains in the show, and his Affably Evil personality provides a humorous contrast to said power. He could've been an interesting new Big Bad, but he is quickly dealt with and is back to Gunther by the end of the episode he appears in. There are a few scattered references to Gunther being Orgalorg every now and then, but it's never truly touched upon again.
Zander, the villain is introduced as a Sheltered Aristocrat with a human side and a genuine, friendship with Terry and Max but in the second half of the two parter, this aspect of the character vanished. While still important he was just a standard villain who ultimately turned into a dinosaur and anticlimactically died, the humanizing aspects of the character gone. Bruce Timm critiqued this on the episode's DVD commentary.
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.
While the show was great at introducing characters, it struggled with following up. Killer Croc, for example, only appears in team-ups after his debut. Poison Ivy has two episodes and is then relegated to voiceless cameos for the rest of the show (fortunately, the tie-in comics realize most of her potential). Catwoman was one of the characters that nearly everybody agreed was handled better than in B:TAS, but only appeared in three or four episodes. One of the reasons Joker and Penguin were so contentious was because they were perceived as being overused in comparison to the rest of the Rogues Gallery.
Bane is a particularly tragic example. He gets used in one episode (which is regarded as being one of the better and more faithful to the source material adaptations of Bane, design aside), and then only gets a couple voiceless cameos where he gets jobbed. The next time Batman goes up against a muscular supervillain who actually poses a threat, it's . . . Joker, using Bane's Venom.
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.
Its sister show, Adventures of Sonic the Hedgehog was also prone to this. There were numerous entertaining characters throughout the series, most of them lucky to appear more than once or even outside a cameo:
Robotnik's earlier henchbots from the pilot episode are perhaps one of the most incredulous examples of the trope. Despite SEGA Of America finding many of their gimmicks and designs worthy to place in Dr. Robotnik's Mean Bean Machine, the majority did not appear outside a very brief cameo. The show frequently utilised other interesting new robots, or even adapted some from the games, Very few of them made recurring appearances.
Princess Sally, in heavy contrast to her Satam counterpart. She was adapted for the Christmas Special, Sonic Christmas Blast, albeit for a non speaking cameo.note Due in part to the contractual obligation of voicing Lola Bunny in Space Jam, Kath Soucie was unable to reprise her role as Sally, and as a result, Sally gets no speaking lines and plays very little role in the plot.
Other antagonists such as Dr Quark and Dr Warpnik could have served as good alternative foes for Sonic and amusing Sitcom Arch Nemesises for Robotnik. They appeared for one episode each.
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...
Had this show used DCAU Tim Drake instead of Dick Grayson, it would've made the series even better.
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. Due to the small collection of human faces its even implied that he can venture outside of the spirit world or somehow lure people in. This leads to 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. With Season 2 of The Legend of Korra titled "Spirits", there was some hope that he'd show up for at least a cameo, but no dice, and even when the end of Season 2 had the portals to the spirit world permanently open, allowing spirits to travel freely into the human realm, he doesn't appear.
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.
Badass Normal Suki. Despite proving herself to be strong and a perfect match for Sokka then joining the Team in Book 3, she stays Out of Focus as the second half of the season is more about Zuko trying to gain the trust of his former enemies. It seems like the writers forgot about her since she's never alluded once in The Legend of Korra (beyond the briefest of appearances in a still image that accompanied Tenzin's introductory narration in the first episode).
Ty Lee gets this even worse than Suki. We never do learn that much about her and she only really shows up three times in season 3, one of which is more of a brief cameo.
Ghazan and Ming-Hua are prominent members of the Red Lotus, plus Aiwei yet have zero backstory for their motivations when even P'Li got a moment of exposition as a former living weapon rescued by Zaheer.
AsamiSato to the extent that every season and Turf Wars underuses her despite having the personal and thematic potential to be Deuteragonist to Korra, let alone how her being in charge of a MegaCorp is only important when the plot needs it to be:
In Book 1, her perspective as a non-bender against the Equalists and the fact that one of its most prominent members is her father, but no, that largely gets overshadowed with her just scowling in the background while Mako fawns over Korra despite still officially being with Asami.
In Book 2, she's AWOL for a number of episodes, now in charge of Future Industries except its reputation's been tainted by her father's actions as well as not interacting much with Korra despite her own parental issues to instead be Chickified to not have even one hand-to-hand fight that season and instead rebound to Mako and doesn't even rescue her own company, leaving that up to Bolin to the extent she's spectating the battle for her own company like it's just another Pro-Bending match!
While Book 3 fixes most of the above problems, she still inexplicably gets less dialogue (in quality and quantity) than Mako, her company's only mentioned in providing a Cool Airship and that she regained full control after Varrick was captured, otherwise she's somehow free to globetrot with the rest of the team.
Book 4 then gives her somehow more to do in using Future Industries to repair Republic City, deal with her estranged father and her romantic feelings for Korra yet less screentime to focus on any of that as Mako babysitting Prince Wu gets more screentime andVarrick'ssudden Heel–Face Turn who's not even part of the main cast yet gets more screentime than half the main team despite the fact that Asami's also personally recruited to design a weapon to counter Kuvira's Spirit Energy-powered one. She doesn't even get a new outfit like the rest of the team!
And lastly, in Turf Wars, not only is there the same problem with Future Industries, but also the fact that she spends two-thirds of the trilogy holding the Distress Ball with the first being to reveal to her friends that she and Korra are a couple and the second because its the cliffhanger to Three-Act Structure.
My Little Pony Tales had Logan Barrington who was the deciding factor in the girls' argument on whether or not to allow boys into their club. Logan could have gone on more adventures with the girls or made other key contributions to the group. However, after he gets inducted by the end of his featured episode, he never makes another appearance in the series.
While "perfectly good" would be a strange way of stating this, Mac's brother Terrence was Demoted to Extra after the first season and eventually became Out of Focus during the fifth and sixth season. What makes Terrence fits this trope is the fact that he never got to appear enough times to develop as a character to explain his cruel treatment towards Mac and in general, and he was never given any redeeming qualities. The case can also be said for Mac's whole family as well since there is never a deeper point of view for Mac's mother and any explanation or even tiny hints of the whereabouts of his father. Keep in mind that Mac is one of the two protagonists. So him not having a deeper family background is an anomaly.
Duchess was the main antagonist of the pilot movie who stood out amongst the inhabitants of Foster's as being one of the few truly hideous imaginary friends in both appearance and personality. She would have made a great major antagonist for the rest of the series (especially given her hatred of the main characters and Foster's itself), but after the pilot however, she's almost entirely Demoted to Extra and only makes sporadic appearances afterwards.
Memnock and Zenblock, despite being main characters got this treatment. Some fans thought that they should have been the lead characters of the show instead of the Noobs. They have a borderline lack of day in the limelight plots featuring them and they were frequently shoehorned into boring and forgettable subplots. While they did get more focus and screen time in season 2 and had part of their backstory revealed through their mentor, Chiquadotran, the show continued to shoehorn them into unnecessary subplots.
Amy Anderson is Tyler Bowmans's love interest but the romance is only half baked and seen in only seen in few episodes. Some people think of her as a scrappy character while others wanted her to be a Sixth Ranger. Even worse was that her relationship with Tyler was only focused on for one episode in season 2.
Many one off characters got this too such as Princess Parsa, The Incredibly Amazing Man, and Marty Soulpatch to name a few.
The Avengers: Earth's Mightiest Heroes underwent a Retool in its second season to increase focus on the BigThreeAvengers, at the expense of Avengers who had yet to receive solo movies at the time. Since The Vision had only recently joined the team before this retool took place, a fan might only need one hand to count the number of episodes in which he does something important.
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 have been a cool non-Deedee companion to Dexter, but he sadly never evolved beyond a Satellite Character.
Olga/Lalavava, Mandark's little sister. She appeared once and was never seen or mentioned since. Made even more bizarre because the end of her episode pretty much confirmed that we'd be seeing more of her.
Danielle "Dani" Phantom, the 12-year-old Opposite-Sex Clone of the title character. 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. In fact, Word of God says that Danielle would have eventually been adopted by Danny's family if the show went on longer, with Danny serving as a Big Brother Mentor to the younger halfa.
The most beloved episode of the show by both fans and the creator, two-parter "The Ultimate Enemy", featured Dark Danny: an evil fully-ghost version of the title character. Being the most amoral character in the show, having spent 10 years ravaging both Earth and the Ghost Zone, his reign came to an end when he's captured in a Fenton Thermos and left in a room outside of the time stream. The episode implied that he'd someday escape, but this never occurred.
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 similar 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.
Raf is an example. Introduced as a computer prodigy able to actually make Soundwave take notice and the ability to understand Bumblebee, he had a few good episodes and characterization in season 1. He was even the catalyst for a Roaring Rampage of Revenge by Optimus Prime. But while fellow human Jack went on to become an honorary Prime and Miko all but joined the Wreckers, Raf faded into the background, relegated to only getting screen time so he could work with the computers.
Hardshell the Insecticon is another example. His backstory gave him a personal feud with both Bulkhead and Wheeljack, setting him up as a new archenemy for one of them, while his physical power let him serve the currently empty slot of The Brute. His personality not only set up some interactions among the Decepticons, but also served as the first view into the world view of the Insecticons. His first appearance has him face off with Bulkhead in several awesome confrontations, cumulating in him crippling the Autobot. But despite the many things that would have made him an interesting character to keep around, he gets killed off in his second episode.
Glowstrike was introduced as one of the most powerful Decepticons aboard the Alchemor and a member of a triumvirate with two other prisoners using the wreckage of the ship as a base. She leads one of the largest and most organized villainous factions in the show. Unfortunately, she is deposed by Steeljaw before she even meets the heroes face to face and we only get the barest inkling at what her powers actually are.
The Autobot High Council are the show's final antagonists and introduced as working against the heroes early on. However, they do not appear in person until the series finale and otherwise spend almost the entire show offstage, serving as an excuse for why Bumblebee and his team don't have any support in dealing with the Decepticons.
Fracture was one of the most dangerous Decepticons introduced in season 1 and also one of the few Decepticons who was not an Alchemor prisoner. He was a Deployer, eternal rival to Drift, and served as one of the more competent members of Steeljaw's Pack. However, after being defeated by Optimus offscreen in the Season 1 finale, he never appeared again aside from a series of shorts that portrayed him as a Butt-Monkey.
While Batman: The Brave and the Bold was admittedly meant to focus on lesser known heroes and villains of the DC Universe, some fans are still remiss that 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. Even in the tie-in game Young Justice: Legacy that shows the circumstances of Tula's death, she stays the entire game in the cave doing nothing but monitoring the team and giving expositions before getting abducted by Klarion at the end and then she does a Heroic Sacrifice to seal Tiamat.
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, a later cameo by Wotan, and Ultra-Humanite joining The Light in season 3, complete with a Creator Cameo by Greg Weisman, never show up again. Most of them wouldn't be out of place in the Light's leadership as proven with Ultra-Humanite, but nonetheless, most of them don't even get lines, with most of their dialogue going to the Joker.
Ruby Rocket Private Detective. Despite the positive reception and very lush animation style, there only exists the single short.
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.
Scruffy is one of the employees of Planet Express, who are the main characters of the show, but he didn't have as much screen time as his coworkers and has an extremely vague backstory. Even his own coworkers forget that he exists frequently. There were plans for him to get an Origins Episode in the final season, but they were scrapped.
Lrrr, the ruler of Omicron Persei 8 is also an example, as he does have a fan following and his voice actor, Maurice Lamarche, won an Emmy award for his voicing of Lrrr. However, he only appears in one to two episodes per season, and they alway either focus on him invading Earth for ridiculous reasons or focuses on him attempting to repair the cracks in his marriage with his wife, Ndnd.
Jrrr, who is Lrrr's son, also got a huge amount of this treatment as well. He appears as a newborn in a season 2 episode and plays an important role in it, but he was Put on a Bus until the last season episode "T: The Terrestrial," where he reappears as a pre-teen who tries to steer away from his father's violent ways. His relationship with his mother Ndnd is shown to be vague and flat.
Look at some Invader Zim fanart and fanfiction without any context and you'll come away thinking that Tak is one of the leads. In fact, she only appeared in one episode of the original series, with an ending that left her fate ambiguous, and while she was intended to become a recurring character had the show not been abruptly cancelled in mid-second season, the show's revival via a comic series and eventual TV movie limited her "appearances" entirely to her personality downloaded into the AI of her ship, with the real Tak only appearing for a single wordless cameo in one panel of the Grand Finale issue of the comic.
Teenage Mutant Ninja Turtles (1987) 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.
The sixth season of Teenage Mutant Ninja Turtles (2003) 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.
Also from the aforementioned season, Starlee Hambrath. The sole (good) female character of the season, she was a rather cute, green skinnedGadgeteer Genius and could've been developed more, including interactions with Donatello, due to their similar intelligence or fleshing out her attraction to Cody Jones. However, of the show's 26 episodes, she only appeared in 5 of them, only one of which ("Enter the Jammerhead") focused on her. note However, the reason Starlee appeared irregularly is actually quite understandable; unlike Viral, the season's other recurring female character, she wasn't a fighter in a show that mainly focuses on characters fighting each other. Even Cody eventually got Turtle X so he could actually participate in the action, Starlee couldn't fight worth crap.
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. And then was written out of the show completely within a rather bizarre manner: he was revealed to be a Soviet spy sent to steal the Park for Russian entertainment. He leaves on good terms with the cast, but is more than likely never going to be seen again.
The Dreamstone is quite prone to this, given it has all the conventions of a surreal adventure series with a big magical universe, though favors being a Villain Protagonist series for the Urpney characters the majority of the time:
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 of 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.
"The Daydream Bubble" has a flashback sequence featuring the Council of Dream Makers that the heroes' Dreammaker and Zordrak originated from. Despite amusing designs and a load of potential in terms of background development, none of them returned and even in their single appearance had no speaking roles or importance, the Council referred to only in very vague moments of exposition afterwards.
Thomas & Friends is profound at this due to its Merchandise-Driven drive to introduce lots 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 its treatment of the cast from the original The Railway Series novels (underutilizing major characters such as Daisy but giving more roles to minor characters such as Bertie, Harold and Diesel).
The international engines from The Great Race film have all been stated to only be sticking around for that one film, which automatically caused some fans to view them this way. This feeling was increased to some following the release of the film in UK cinemas, as with the exceptions of Ashima, Vinnie, and the Flying Scotsman, most of them are relegated to primarily background roles, only having one or two lines each with some not speaking at all. One of the biggest offenders is Yong Bao; he's mentioned as having saved hundreds of people from a horrible accident, and he doesn't even get to speak.
Helen's family in Daria were fascinating characters with a lot of potential, and the drama surrounding their sisterly arguments (and Daria & Jake's frightened and frustrated reactions to them) was solid. Not to mention that their fractured relationship was a good cautionary tale for Quinn and Daria’s future. Each of them only appeared a tiny handful of times.
Freakazoid!: Freakazette. A Distaff Counterpart of Freakazoid that appeared for all of 3 seconds in the "Freakazoid and Friends" song in the first episode, yet was never seen or mentioned in the series again after that.
Ever After High features a very large cast of characters (as it's a Merch-based line), which leads to this a lot. Of particular note with many fans is Cerise Hood- the Daughter of Red Riding Hood and The Big Bad Wolf. The fact that her father's identity is a secret is a major plot point for her character, and she has many interesting attributes to the fans (such as her physical skills, her and Daring slowly respecting each other, and her more introverted nature — a contrast to the show's more charismatic cast)... but she's a third-tier character at best, and almost never shows up anymore.
Pacifica Northwest started off as an antagonistic foil to Mabel Pines, but gained more Character Development in the second season, with "The Golf War" and "Northwest Mansion Mystery" focusing more on her life and having her Heel–Face Turn to become one of Dipper and Mabel's friends. Immediately after the latter episode, however, came "Not What He Seems". For the entire rest of the series, Pacifica became heavily Out of Focus due to the story shifting focus on the final story arc surrounding the Pines family and Bill Cipher. Her next role of note wouldn't be until the series finale, where she had to share screentime with a number of other reoccurring characters and had even seemed to regress to her previous characterization. Shippers were especially saddened, as "Northwest Mansion Mystery" teased Dipper and Pacifica developing crushes on each other, which never gets mentioned again in the show (but does get explored in canon side material).
Despite being part of the main cast and appearing prominently in season one, Wendy Corduroy never received much characterization beyond being a cool teenager and the target of Dipper's Precocious Crush. Season two mitigated some of the fans' complaints by having her participate more in the twins' adventures, but not a single episode had her as a focus character. Wendy also never has any on-screen interaction with her father Manly Dan or brothers during the entire run of the show, with a small exception in the Grand Finale.
8 1/2 President Quentin Trembley could've shared a role with Ford as the Big Good but only appeared in the Grand Finale as a cameo in the credits.
Out of all the main characters, Summer so far has the least amount of episodes with her in the limelight. She only got to go on a couple of adventures with Rick by herself in season one and season two pushed her further away. Some of the episodes only had her utter one speaking line. The third season might give her more limelight episodes as evidenced by the trailer.
Scropon appeared as a friend of Rick's in "Ricksy Business" at the house party but he had no speaking lines, only got a few seconds in the spotlight, and was shoved away for the rest of the episode with Rick stating that Scropon was looking sad at the party because his home planet was destroyed. Scropon appeared again in "The Wedding Squanchers" but once again he not only didn't get any speaking lines, but he only filled in the role of one of the background characters and got shot at the wedding, leaving his fate unknown.
Krombopulous Michael made his only appearance in "Mortynight Run" as an assassin and a buyer of weapons from Rick but his friendship with Rick, his past, and motivations for being an assassin are very vague. Plus its revealed that Michael had a girlfriend through a locket he carried with him but the girlfriend never appeared in person nor was she named. To add insult to injury, Michael was killed off simply because Morty was sleeping behind the wheel.
Rick's other two friends, Birdperson and Squanchy are also considered wasted characters due to their lack of appearances despite their friendship with Rick and importance with the shows story arc and the season two finale drastically changed their fates with the former initially murdered then turned into a cyborg and the latter's fate still ambiguous.
Jessica is Morty's primary crush and she got a good amount of appearances in season one. Unfortunately, she goes Out of Focus in season two only having a role in a post credits scene in an episode. She might be going back into focus in season three though.
Snuffles is Morty's pet dog but in the second episode when he gets his first and only major role, he gets Put on a Bus by the episode's end and is not seen again aside from family photos in later episodes.
The president of the Galactic Federation was in the position to be the Big Bad of the series but he was never seen or mentioned in the first and second season. By the time he finally appears in the third season première, he only gets less than a minute of screen time before committing suicide, causing Tammy to take over as the big bad.
The post-credits scene of the Season 3 premier hints that Tammy may become the season's overarching villain. However, she doesn't make any further appearances and doesn't end up fighting Rick.
Terry Gimple of The Cleveland Show. A swaggering Nice Guy, who also happened to be a rare openly bisexual character on television. But after said reveal of his sexuality, he was all but written off the show. Eventually losing his spot in The Team to Flat Character Dr. Fist.
Peedee Fryman. He was introduced in one of the show's first episodes, with said story giving him a good amount of focus and characterization, to the point that it'd be easy to think he'd regularly appear as one of Steven's human friends; his cynical, melancholic personality and feelings of insecurity made him a perfect Foil to Steven's cheerful optimism and (at the time) blissful naivety. Once Connie showed up, fans believed that he would form a Power Trio alongside Steven and her, with Peedee taking an active role in Steven's adventures. Instead, he was quickly reduced to a background character, while other Beach City residents who were less liked, such as his brother Ronaldo, would get far more appearances and dialogue.
Bismuth was the first non-Homeworld character that finally gave Steven (and the audience) a perspective of Rose Quartz, Homeworld and the Crystal Gems that he couldn't get from Garnet, Amethyst and Pearl, who had nothing but idealized memories of Rose and mostly kept Steven in the dark. She was also the first one to tell Steven he didn't have to be like Rose. Her introduction being for a Milestone Celebration special and having a Celebrity Voice Actor resulted in her being treated as being no more than a one episode Filler Villain until returning at the end of Season 5, after which she only acted as a supporting character in the movie and Future.
Hunk. Despite being a major character, he gets the less development out of any of the Paladins, and the majority of his dialogue is to be throwaway lines and comic relief.
The Balmarans. They were the focus of several episodes way back in Season 1, and briefly appeared in Season 2. But aside from that, they haven't been seen since they debuted, though Shay got a brief mention in Hunk's vlog.
Dr. Screwball Jones. The Evil Counterpart to Wander who is a Well-Intentioned Extremist about spreading happiness throughout the galaxy, and nearly managed to succeed. Come "The Battle Royale," however, he ends up losing to Wander in a Curb-Stomp Battle, then losing off-screen to Lord Dominator before "My Fair Hatey" and doesn't even get to sing again in the latter. Justified as the creators mentioned that they had trouble getting Weird Al in to record more lines for Screwball, as Weird Al was very busy at that time, and the staff underestimated his popularity◊.
Major Threat is a badass ex-villain who turned good after meeting Wander, yet he barely shows up outside of "The Good Bad Guy", and never once interacts directly with Wander, despite the two being reunited in "The End of the Galaxy". Apparently he would've appeared more prominently in Season 3.◊
Saffi was a Cloud CuckoolanderCute Monster Girl who made for an amazing romantic partner for Beezy and was the series' biggest Ensemble Dark Horse. She had the potential to become a Breakout Character, but ultimately remained just a recurring character with only a handful of appearances. Then in Season 2, Beezy casually broke up with her as a joke, and she vanished without any other major appearances.
The episode "Pop-Sicles" introduced Lucius Heinous VII and Beezy's ancestors, which was quite well-received by viewers. They had the potential to become incredibly interesting recurring characters who could have contributed a lot of info on the series' setting and characters. Lucius I in particular could have been great for a movie/special as a Big Badnote Word of God even said there were plans for him to appear on the show. However, with the exception of Lucius VI (who was unfortunately underutilized), all of them were only given mentions and non-speaking cameos afterwards, with Lucius I never being brought up ever again.
Atomic Puppet: While Pauline got a decent amount of attention (although admittedly, she could have gotten some more limelight episodes; we never meet her parents or her Cool Uncle who's All There in the Manual), her time as Sword Sister was a missed opportunity. What we saw of her in that episode was pretty awesome on its own, but it would have been even more awesome if she got to remain Sword Sister for the rest of the series (perhaps Princess War Tickle could have trained her to use the Sword of Enlightenment or given her some other weapon), allowing her to assist Joey and AP as more than just as their sassy Muggle Best Friend.
The pair of military guys from Milo Murphy's Law They appear in the opening sequence, but only appeared in four episodes, and it's never revealed exactly who they are or what they do note Except creating cyborg bears that eat man, apparently. The episode "the Note" shows they know about Milo and his problem, so it would have been interesting to see that play out.
Bradley Nicholson played an important role in the first handful of episodes as a grumpy Foil to Milo (with an implied crush on his friend Melissa), but was virtually Demoted to Extra from there as the secondary plot involving time travel became more central, while Knight Templar school crossing guard Elliot Decker began to fill his narrative purpose as a Sitcom Arch-Nemesis. Even having his arm turned into a plant as of the Season 2 premiere didn't do much to pull his character out of irrelevance. Despite this, he remains an Ensemble Dark Horse.
Triana's friend Kim appears in two episodes, one of which she was featured in, the other she had all of a minute of screen time with no lines. May have something to do with her attitude, her potential to become a supervillain, and her possible ships with the boys and Dermott. Fans have been requesting a return ever since. Hank asks Triana about her in the season 4 finale, after having trouble finding a prom date. She says that she's become a born-again Christian and currently lives in Florida. So she's probably not going to show up again anytime soon.
The Groovy Gang, a group of minor antagonists who only appeared in a major role in one episode. They were a dark parody of Mystery Incorporated, with each member being based off of an infamous figure from the 20th century in addition to their Scooby Doo counterpart. Fans generally agree that they had a lot of potential as funny and interesting recurring villains, but they are quickly dispatched by Brock Samson before the end of the episode. However, Ted and Sonny are seen again later as zombies as part of Venturestein's army.
The Grand Galactic Inquisitor gets axed after one episode, despite being one of the funniest characters yet.
The G.I. Joe parody characters (Sphinx Commander and his gang and the unique OSI operatives seen in "O.S.I. Love You") get barely any screen time and mostly serve as Canon Fodder.
Final Space has The Dragon to the Lord Commander, an alien cyborg who resembles a hulking armored one-eyed xenomorph. He's introduced in the first episode being ordered to eat a prisoner that the Lord Commander had just killed, hinting at him being a creepy, intimidating foe. However in the following episodes he barely does anything or even appears, before being suddenly and unceremoniously killed off by Little Cato. On top of that, his name is never even given in-series.
A a tie-in book introduces us to Seth, Toffee's boss who was actually behind his revolt and the death of Moon's mother. Pretty much every fan who knew about him thought that he was going to show up as the true Big Bad of the series, but he's never even mentioned in the show. Interestingly, after the show ended, producer Dominic Bisignano and creator Daron Nefcy gave contradictory information on the character—the former said that he's alive and might appear if the show got a fifth season, but Nefcy said that he was already dead by the events of the series.
Mina Loveberry is an interesting case, since the problem isn't that she was underutilized, but rather, that she was used at the wrong place at the wrong time. She ends up being the final villain of the show, which many fans can agree doesn't work for the kind of character that she is. Mina is nothing more than a Psychopathic Manchild who's obsessed with destroying monsters in any way that she can. She would have worked much better as a recurring villain akin to Ludo, with her potentially even teaming up with Star to defeat a different Big Bad for the finale.
After Toffee's defeat at the beginning of Season 3, Ludo starts to become Out of Focus, appearing in very few episodes from that point on. This made his redemption feel very forced and poorly thought out, especially since it introduces Ludo's brother, Dennis, who is a genuinely interesting and likable character that many fans would have loved to see more of.
Quite a few people wish that Mort had more significant appearances in the show. While he was fairly prominent throughout the first three seasons, after that he appeared less frequently and often only had a few minor appearances per season.
Jessica from "Slumber Party", the only kid who doesn't end up dropping out of the sleepover and shows a lot of cunning, enough that Louise considers her a Worthy Opponent, but she took a long time to make her second appearance. Years later, they brought her back in "Three Girls and a Little Wharfy" in the tenth season.
Josh from "Lindapendent Woman" was pushed as a possible love interest for Tina, which was expanded into a Love Triangle with Jimmy Jr. in "Two for Tina". However, following this, Josh would abruptly vanish from the show and wouldn't return until Season 10's "Tappy Tappy Tappy Tap Tap Tap"... at which point his relationship with Tina was abruptly sunk with little foreshadowing.
While Disney's adaptations of the Pooh franchise generally thrive on an Ensemble Cast dynamic and giving every key character some moments in the limelight, Kanga is often noted to be the exception, getting almost zero spotlight stories in any films or TV shows and generally remaining an Out of Focus mother figure. While Kanga was to some degree the least focused in the books as well, she was still often among the main cast and plots.
New Adventures of Winnie the Pooh in particular introduces several original characters who had potentially fun dynamics among the main cast. Most of them only appeared once or twice. One of them, Kessie the bluebird, was revived for the later show The Book of Pooh however, where she appeared much more frequently.
Debbie Hyman, for she was the first girlfriend Steve had for more than one episode. Unfortunately, she was never really given much development beyond that, most of her appearances ended with her and Steve breaking up and she was often used as a target for cheap jokes regarding her weight or monstrous appetite.
Akiko Yoshida, yet another romantic interest for Steve who appeared more than once. Like Debbie, she never received any significant development beyond being Toshi's translator (initially) and a girl that Steve happened to have a crush on. She finally gets more development in "Spelling Bee My Baby", which sees the two officially becoming a couple, only for her to abruptly disappear in the following episodes, leading Steve to become single once more.
Linda Memari, who was written to be Francine's friend. Additionally, she has a secret crush on Francine (although her husband Bob is aware of it), leading to an Unresolved Sexual Tension. This was never brought up again, since she's pushed to the background through the rest of the series. And in one episode, Roger claims that she died.
Season 2 introduces Frobo, a robot who is particularly close to Polly. Despite being accepted into the Plantar family, he really doesn't do much throughout the entire series and probably could have been written out entirely. Being a Fish out of Water just like Anne, there could have been some dynamics between him and Wartwood. Since he's also a robot, there could have also been some interesting dynamics between him and Andrias's army.
Despite being the Final Boss, there are still some who feel like The Core could have made for a better villain. They really only start to have relevance in the final few episodes, and their backstory isn't really fleshed out. How did they come to be? Who is part of it besides Aldrich? What is their ultimate goal in taking over the universe? The world may never know.
The episode "If You Give a Frog a Cookie" introduces Dr. Frakes, a Mad Scientist who figured out how to create a portal that leads to other worlds and wishes to learn more about alien life, which includes dissecting them. It could have been very easy for her to enter Amphibia completely on her own. What would have happened if she ended up on an "alien planet"?
Percy and Braddock are the only toads who stayed loyal to Grime and Sasha after Toad Tower was destroyed and Grime lost his position of power. They are seen accompanying them for most of Season 2, but after Sasha forces them to go on a deadly mission even after they told her that they didn't want to, they end up leaving them, and they aren't seen for the rest of the series aside from a cameo. What happened to them after Sasha and Grime learn from their mistakes and Sasha ends up becoming someone worth following?
Eugly was repeatedly shown to have Hidden Depths to her character, as well as dating Quack-Quack, one of the main characters. An entire episode was also dedicated to her befriending Mr. Cat and Stumpy. Despite this, she continued to receive little screentime during her time on the show, and in the show's fifth season she was Put on a Bus and reduced to cameos.
Season 5 introduces us to Stumpy's little sisters, each of whom get one episode entirely dedicated to them. One of them is Ardoise, who is clearly affected by the bad circumstances that life has put her through and is significantly more mature and responsible than her other siblings. However, Ardoise's focus episode ended up focusing on Stumpy and Pretty while Ardoise herself functioned as a plot device rather than being at the forefront of the episode, which was especially poorly received by fans due to Pretty's status as The Scrappy in this season.
Garby to some extent. He is the Sixth Ranger and yet sometimes show treats him like a secondary character. Best example is the final episode when he's not with the rest of the gang, when they come assist Ty who is fighting D-Structs in volcano. What's weird is that Xee who's also a Sixth Ranger does come with them, but not Garby.
Gold Trux. He has unique design than other villains featured in show, quickly establish himself as dangerous threat to Ty and crew, and his past with Garby could've resulted in exploring Garby character. Instead, he only appears as Villain of the Week, with no mention of what happened to him after the events of his debut episode.
Rhonda is revealed to be an spy of Dr. Blowhole at the end of her episode, but that's never mentioned again and even when she comes back in "The Hoboken Surprise", this is not mentioned nor does she have any major role.
Hans's role in Skipper's Dark and Troubled Past is never touched upon again after his first appearance, because of this he becomes just another villain in the Penguin's Rogues Gallery from that point onwards, despite the fact he's meant to be Skipper's Arch-Nemesis and therefore could have bringed more personal stakes when they faced him. One later episode alludes to the backstory, but his present self is strangely absent of that episode.
Blue Hen is another villain with wasted potential; she's basically an Evil Counterpart to Kowalski, being a bird so insanely intelligent that she was able to predict the movements and actions of all the animals in the zoo and participants in sports teams, with enough ingenuity to create a plan that would turn her into the president. With this amount of intelligence and skill, she could have easily been one of the Penguins most dangerous enemies. Sadly, she's not much of a threat in neither of the episodes she appears in, and her rivalry with Kowalski could have been developed more.
The Danish security chief could have being a great recurring antagonist, being both an hypercompetent human aware of the Penguins activities and being tied up to Skipper's past in the same way Hans was. But alas, the episode where he made his first appearence happened to be one of the last episodes produced before the show was cancelled.
Executive Meddling caused the special "The Penguin Who Loved Me" to unintentionally become the ending of the series. Because of this, the handling of certain characters is a bit of a letdown for a Grand Finale.
Despite being main characters as well, the Lemurs only appear in the intro and in a small gag, while Marlene is nowhere to be seen. They do, however, play a role of importance in the previous special, "Operation: Lunacorn Apocalypse"
As noted in Anti-Climax Boss, Dr. Blowhole's final outing doesn't amount to much, despite being a Knight of Cerebus in his previous appearances. He basically recovers his memory, then Kowalski annoys him enough time to distract him and kick him, and that's pretty much it. Given the special ends with a And the Adventure Continues note, chances are this wasn't meant to be the end of the character, which leaves the final fight of the Penguins against their biggest rival end in a rather unsatisfying note.
The Reveal that Manfredi & Johnson are still alive is reserved for a quick joke. Despite this opening a whole new can of potential stories.
Chaotic Evil). Second, he used magical items as opposed to technology. Third, he and Jazz both shared "Ghost Envy", giving them a similar 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.
song in the first episode, yet was never seen or mentioned in the series again after that.
