Flanderization

Flanderization is a trope that refers to the act of taking a single trait from a character and exaggerating and amplifying it more and more over time until it completely consumes the character. Most always, the trait/action becomes completely outlandish and it becomes their defining characteristic. Sitcoms and other comedy shows are usually the ones to suffer from this, due to the writers doing anything they can to get a cheap laugh from the audience, even if it means sacrificing a character's personality. Either there are out of character personalities that are counted as against the characters we know and love, or there are personalities that will make you have no choice but to lose all of the respect you had for the characters.

Although, flanderization doesn't always make the characters turn out awful. Sometimes flanderization can make them funnier and likable. It depends on how the character is flanderized. This good side of flanderization is most noticeable in Thor from the MCU, who became a less serious and more badass hero.

Flanderization is especially common amongst works where the creator is not involved, with their replacement not understanding the nuances of the characters and what made them so good in the first place, even if the lore was explained to them or had seen the series when the creator was involved. It is also extremely common in fanfiction for similar reasons no matter how devoted a fan is.

The Simpsons, being the series which spawned this trope's very name, has this almost across the board. Over time, the series has, in many ways, become a symbol of this trope in its purest form.

In the topic of flanderization, the American animated sitcom King of the Hill is a notable example of a series that used flanderization. This series is known for giving flatter characters new aspects, then focusing on them, thus creating the sense of flanderization at the same time as they get mh:greatcharacters:character development.

Flanderization is to not be confused with character derailment, in which it involves a character's trait(s) being vastly different compared to what was previously shown.

Although rare, some characters have actually recovered from flanderization overtime, like The Simpsons characters, Batman (DCEU), Superman (DCEU), Ben Tennyson (2016), SpongeBob SquarePants (Seasons 6-8), Patrick Star (Season 7) and Gwen Tennyson (2016).

Notable Victims of Flanderization
NOTE: If highlighted in green, it is positive flanderization.

The Simpsons

 * Ned Flanders (The trope namer, as he went from simply enjoying going to church to being obsessively religious and overly nice, and then religious fanatic who will lash out at anyone who doesn't support Christianity.)
 * Moe Szyslak (He started as a rather grumpy bartender who will do anything for money, including resorting to do behind the scenes illegal activities that were mostly played as jokes (such as smuggling animals for unknown reasons), and while he was short tempered, he was still a good person at heart, he was simply a grumpy man living in a disappointing life and to improve it, but later on, his actions tend to be more criminal as at one point, he became a registered sex offender, and encouraged alcoholism, and is part of a running gag was he tries to kill himself but fails.)
 * Homer Simpson (Seasons 16-30; he went from a dimwitted, yet well-meaning father to a moronic idiot who sometimes acts like a selfish jerk, and became even dumber, and more of an aggressive alcoholic with no control over his emotions, as he would burst into tears or throws tantrums on a regular basis.)
 * Marge Simpson (Seasons 16-30; She went from a loving, prepared, down to earth and strict mother to being a really overprotective mother worries too much about everything and is extremely boring and un-impulsive by nature, getting hyped up by household chores and monotonous hobbies. By the HD seasons, she's also become more of a jerk, particularly towards Homer.)
 * Bart Simpson (Seasons 11-31; He went from a mischievous kid as he loved causing trouble and didn't respect authority, but he wasn't an inherently bad kid, and he had conscience of preventing himself from doing something really bad into a borderline sociopathic jerk, as he didnt care about the health, safety, and lives of anyone, even his own family, as long as he could get some laughs, luckily he still gets his comeuppance for his antics sometimes.)
 * Lisa Simpson (Seasons 11-31; she went from a level headed foil to Bart and was the smartest and the most well behaved out of the family, and was the voice of reason type of character to a complete know-it-all and a political soapbox as she was start complaining about anything that didnt meet her high standards, and was the only one to protest against the injustices she perceived around her.)
 * Maggie Simpson (She went from a character who occasionally has plot relevance (such as her shooting Mr. Burns in "Who Shot Mr. Burns?), but she later had some individuality, into simply a background character who only exists for filler.)
 * Otto Man (He went from a cool and laid back bus driver to a dangerous low-life and a drug addict.)
 * Patty and Selma Bouvier (They went from simply making mean jokes about Homer to being full-on sociopaths who wanted to see Homer suffer. Even going as far as to urge him to jump off a bridge in "Eternal Moonshine of the Simpson Mind" and kidnapping him and locking him in a dirty bathroom in "Wedding for Disaster". Later seasons tone this down though.)
 * Seymour Skinner (Seasons 16-30; he went from a reasonably competent, no-nonsense principal who was a Vietnam veteran and had an overbearing mother, and was one of Bart's enemies, as he tried to force authority on Bart, to a pathological and pathetic wimp who at one point, tried to convince Springfield that he was still a virgin though he lied about it to deflect from accusations of improper conduct with Edna Krabappel, and became even more wimpier as whenever he tries to assert authority on his students, such as Bart.)

Family Guy

 * Peter Griffin (Season 8-present; he went from a from somewhat of a jerk yet ultimately cared about his family, and was incredibly respectful to Meg (one episode involved him saying he'd take a bullet for her) and was also a silly doofus and likable father overall into a malicious, idiotic, monstrous, and incredibly abusive and insensitive psychopath who does illegal and evil things in almost every episode and is always excused for his actions as he's said to do that stuff out of idiocy, even though that's not true. He is also a rotten friend, having shot Joe in the eye and Quagmire in the arm on two separate occasions.)
 * Lois Griffin (Season 8-present; she went from a a nice and compassionate wife of Peter Griffin to a short-tempered, immature and psychotic dominatrix wanna-be who sometimes abuses Peter, acts like she has control over her family's life, is a massive hypocrite who calls Peter out on things "she's" guilty of, and is very loud and obnoxious. She's an even bigger Karma Houdini than Peter.)
 * Meg Griffin (Seasons 8-14; she went from a a normal girl wanting to make friends to getting routinely abused, until she finally snapped, such as trying to plan sexual assault on Chris just so she could have closure from a gay boy, going all Fatal Attraction on Brian, trying to replace Bonnie as Joe's wife by framing her and breastfeeding their baby, or engaging in a deadly fight at the school cafeteria. However, since Season 14 she's been abused less often.)
 * Chris Griffin ('Season 8-present; he went from a normal, kind, slightly-dimwitted teenager who is an incredibly talented artist to a completely-dimwitted, uninteresting character who's only known for just masturbating all the time, known for going full idiot mode and is only used when Peter has had too much screen time. But he didn't see too much decline in character, and kept most of his charm.)
 * Brian Griffin (Season 8-present; he went from a sarcastic and snarky talking dog who was the voice of reason, and was the most intelligent out of the family to a self-absorbed, pretentious, alcoholic, egotistical douche-bag and "occasionally" atheist fundamentalist (in other words, essentially Seth MacFarlane's political soapbox) that tells lies to get attractive women to like him, thinks religions are purely evil, and their followers are idiots even though not all of them are like that. He is a conniving and ungrateful scoundrel who will do anything to advance any of his careers, especially if it means hurting his loved ones, screwing over the people who helped him, or letting people die. He's also a massive hypocrite by saying Lois having an affair with anyone other than him is wrong. his entire personality now amounts to being a "liberal", and became a complete jerk and got even worse when he came back)
 * (He went from a toddler with the mind of an evil genius to a toddler with the mind of a stereotypical gay guy, but later returned back to how he was. Depending on your view, however, you could see this as character development since Stewie is no longer evil and has changed his ways, making him seem more likable).
 * Glenn Quagmire (Season 8-17; he went from a funny and somewhat perverted ladies' man to a complete pervert who is used for little more than sex humor and has his perverted qualities exaggerated, though he redeemed himself in Season 18. became not just a pervert, but an implied child molester, though he did redeem himself).
 * Cleveland Brown (The Cleveland Show (Season 1); he turned from being a kind, well-meaning guy to being essentially the black version of Peter Griffin, though in season 2 onwards, he redeemed himself.)
 * Joe Swanson (Seasons 8-present; he went from a strong and confident police officer who was a good role model, and did manage to be a skilled and competent character, despite not being able to walk to a crutch for cruel handicap jokes, an old groaner who screams way too much, and a cowardly spineless cop who lets Peter get away with everything and never arrests him for any lawbreaking acts like shooting Joe in the eye with a BB gun, and for giving his daughter a raspberry in the "wrong place." What also doesn't help is that in the newer seasons, he gets way too much screen time. It's like the writers have a new motto: when in doubt, shove Joe into the scene.)
 * Bonnie Swanson (Seasons 8-present; in the earlier seasons, she was Joe's caring and supportive wife, but in Seasons 8-present, she now sees him as an inconvenience and someone to bully, cheat on Joe and kill him. The biggest example of Bonnie wanting to cheat on Joe is the episode "Foreign Affair" which the main plot of the episode is Bonnie wanting to have an affair in Paris.)

The Garfield Show

 * Garfield (While in the original incarnations, he was always a jerk, but in this series, he became more of an unlikable slob with little to no redeeming qualities. He's also a hypocrite, as he stated in one episode he didn't like bullies, despite the fact that Garfield bullies Odie, Jon, and Nermal all the time.)
 * Jon Arbuckle (He became more of a bumbling, idiotic, and unlikable jerk who was mean-spirited towards Garfield and later Odie).
 * Nermal (He was an arrogant, yet cute, innocently gullible and lovable cat into a despicable jerk, even worse than how he's portrayed in the direct-to-video trilogy. He was at his absolute worst in "King Nermal".)

Teen Titans Go!

 * Robin (Teen Titans Go!); (he tends to act like a dominant and severely paranoid, arrogant jerk, especially towards Starfire, rather than being a strict team leader. Not helping matters is that he is also treated as a Butt-Monkey at times, as his subordinates often act disrespectful to him, even whenever he is in the right.)
 * Starfire (Teen Titans Go!); (she also tends to act more immature and childish, and screams a lot in a way as if Hynden Walch is screaming at the top of her lungs. She also adds "the" into many of her lines of dialogue which can be really annoying)
 * Beast Boy (Teen Titans Go!); (while in the original, he was always portrayed as childish, but he was also quite serious, but in this series, he is now an immature, whiny, destructive, literal party-animal teenager and a lazy couch potato who barely gets up to do something simple.)
 * Cyborg (Teen Titans Go!); (he like Beast Boy, became an annoying and idiotic slacker, with his giraffe neck gag being annoying at times.)
 * Raven (Teen Titans Go!); (she went from a gothic and short-tempered, yet caring to emo, depressed and disastrous, and is more prone to fighting the other Titans whenever they annoyed her, especially Beast Boy.)

Ed, Edd n Eddy

 * Ed (Seasons 5-6; He went from the muscle of the group who's a bit of a simpleton filled with hilarity to being a too dumb to live-type character who is overly emotional and excessively obsessed with gravy.)
 * Edd (Seasons 5-6; He went from being the brains of the group who's a bit shy and awkward to being a constantly complaining goody two shoes.)
 * Eddy (Seasons 5-6; He went from being the self-appointed leader of the group who's a bit devious and ill-tempered yet effectively encouraging with his driving force on giving his friends guidance to being a loudmouthed, problematic, unsympathetic and obnoxious maniac.)
 * Jimmy (Seasons 2-6; He went from a nice and cute child to a whiny, vengeful and accidental-prone crybaby who always gets pampered by Sarah.)
 * Jonny 2x4 (Ed, Edd n Eddy; Seasons 2-6; He went from a loner, yet imaginative and free-spirited kid who was an occasional ally of the Eds, into an annoying, loudmouth and unfunny goofball plus saboteur who can't act or function without Plank's input and presence.)

SpongeBob SquarePants

 * SpongeBob SquarePants (Seasons 6-8; He went from being a naive, eccentric and somewhat immature, yet optimistic and well-meaning protagonist who has some moments of maturity every now and then to being an even more immature, annoying, outright troublemaking, and obnoxious idiot who is either too happy or a crybaby, and annoys other characters for no discernible reason such as Squidward Tentacles, his restaurant co-worker and one of his two neighbors, and Mrs. Puff, his driving teacher. became an obnoxiously happy moronic idiot and a crybaby in some episodes. However, in the season 9-present seasons, he did redeem himself, and went back to his old personality, due to complaints from fans and critics.)
 * Star (Seasons 1b-5; 6-8; he suffered two flanderizations; he started out as a kind of dumb but fairly intelligent, but as Season 1 progressed, he became more stupid and immature and eventually his stupidity became his main, defining trait (this can be seen as a good flanderization, as some of his quotes are memorable like "Is mayonnaise an instrument?"). Unfortunately, in Seasons 6-8, he had a second Flanderization (which ruined his reputation temporarily). He essentially became brain dead, with his actions becoming dangerous at times. He also became a selfish jerk. True, Patrick had his jerky and antagonistic moments in earlier seasons, but these moments pretty much became a major part of him in these seasons. Then, in Season 9 onwards, he did redeem himself, and went back to his old personality, after years of complaints from fans and critics)
 * Mr. Krabs (Seasons 6-8; he went from a greedy yet goodhearted restaurant owner to a more black-hearted and self-serving greedy monster who, in one episode, terrorized Plankton to the point where he attempted suicide (yes, seriously) and Mr. Krabs just brushed it off like it was nothing; his love for money also became over-exaggerated, and while he did not fully recover from flanderization, he is more tolerable in season 9-present)
 * Pearl (Seasons 6-8; In the earlier seasons, she was emotional, yet still likable teenage girl, but in these seasons, she became an extremely whiny spoiled brat who always wants very expensive things as well as being an annoying crybaby similar to SpongeBob. Speaking of SpongeBob, Pearl does not get along with him very well in these seasons compared to the first five seasons.)
 * Plankton (Seasons 6-8; became a bigger punching bag than before just like Squidward, where bad things happen to him, even when he doesn't do anything wrong. He's also a less effective villain, particularly in Season 6.)
 * Karen (Seasons 6-8; In the first five seasons, she was loyal and devoted to Plankton, if a bit snarky at times. In these seasons, she is defined by her snarky demeanor, to the point that she rarely has anything supportive to say to Plankton, even when he's on the brink of suicide. She often gets frustratingly aggressive with Plankton's attempt to outstage Mr. Krabs.)
 * Sandy Cheeks (Seasons 5-8; She became a lot more obsessed with science than her other traits (eg. karate and Texas), even more so than in Seasons 4 and 5, up to the point where she's become a bland, one-dimensional and neurotic science geek with no interesting personality whatsoever. While she did have an interest in science in the first four seasons, it wasn't her defining trait back then.)
 * Squidward Tentacles (Seasons 6-8; He became a constant grouch to everyone and everything around him, showing little care towards SpongeBob or anyone else. In the earlier seasons, he was quite grumpy, but had a good heart inside and would defend SpongeBob if he was in the right. He is also used as a punching bag in a ludicrous amount of episodes that there are too many to list, see some of them below. In these seasons, as well as the modern seasons, he is often just hurt for no reason, when earlier in the show, he would try to do something bad to SpongeBob but it would backfire and hurt him instead.)
 * Mrs. Puff (Seasons 6-8; She became a much bigger punching bag than she was in the previous seasons (more so on that latter), even if she is unlikable at the correct times, such as Demolition Doofus.)

The Fairly OddParents

 * Timmy Turner (Seasons 9-10; He has gone from a tragic and unpopular, yet goodhearted kid who just wanted his life to be better into a selfish and bratty jerk who only cares about getting what he wants.)
 * Cosmo and Wanda (Seasons 9-10; went from a cute and loveable fairy god couple with the former being simple-minded, yet charming and the latter being the intelligent, yet voice-of-reason into a generic idiotic husband and nagging wife stereotypes who shared an equal amount of stupidity and carelessness, while frequently losing their wands for what can only be described as plot contrivance.)
 * Mr. and Mrs. Turner (They started out as busy and clueless but soon became extremely negligent parents who have hinted at times that they don't truly love Timmy, and see him as a burden. This was actually the plot catalyst in an episode with a parody of the late Steve Irwin, called 'The Bad Parent Hunter'. While their characterizations were never perfect from the start, they were more tolerable in the first five seasons aka the classic era. Mr. Turner, in particular, has worsen as the show went on, especially in the final two seasons, due to the "Idiot Dad" trope being severely overused on him similar to Cosmo and the fact that he acts like a complete child. Mr. Turner's screen time has also been unbelievably increased in the final two seasons, usually for humor's sake.)
 * Vicky (Seasons 6-10; went from a sadistic bully who enjoys torturing Timmy while keeping him safe, to a psychotic killer who wants to outright kill Timmy for no apparent reason while also having a severe reduction in screen time despite still appearing in the intro of the show.)
 * Tootie (Seasons 6-7; went from a nerdy, yet nice girl who has a crush on Timmy and occasionally helped him to an obsessive, lovesick stalker who constantly harasses Timmy whenever she sees him.)
 * Denzel Crocker (Seasons 9-10; went from a crazed teacher wanting to prove the existence of fairies to the world into just another annoying manchild like what Mr. Turner has become as well as an incompetent and idiotic villain while being shoehorned into almost every episode, usually for humor's sake like Mr. Turner.)
 * Jorgen Von Strangle (Seasons 9-10; started out as an intimidating and lawful antagonistic fairy ruler, but as the show went on, he got dialed down to being more of a supporting role. Depending on your view, you may find this as an actual development in character. However, at times, this also made him more of a wimp as evidenced in "Teeth for Two". Then by Season 9, he was dumbed down to just a generic plot device whenever the writers needed to bastardize Da Rules.)
 * Foop (Seasons 9-10; He started out as a villain wanting to destroy Timmy and his fairies in his Season 7 debut, "Anti-Poof". But as time went on, he himself has also seen some levels of inconsistency within his characterization here and there, in which he has become less of a villain and more of a pointless moronic comic relief in the same way as Mr. Crocker.)
 * Dark Lazer (Seasons 9-10; He, like Foop, started out as a villain wanting to destroy Timmy, his fairies, and the town of Dimmsdale, into an incompetent and idiotic villain in one episode in Season 10, followed by a typical heel-face turn villain in his remaining two appearances afterward.)

South Park

 * Eric Cartman (Season 20; He acted uncharacteristically wimpy for the entire season. While the writers mellowing out Cartman's character is not all that bad of a concept, it was just executed rather poorly, as they did not go anywhere with it, and it is never even explained why Cartman was acting so differently. Normally changing a character is fine, but it has to be coherent to the story and the development must be gradual, something that feels earned over time. Cartman's characterization in this season totally comes out of nowhere.)
 * Wendy Testaburger (Seasons 7-17; she went from a kind-hearted girlfriend who is having an adorable date with her boyfriend, Stan to an irredeemable bitch who's mean towards girls and boys (mostly Stan, her boyfriend) which makes her very unlikable and worse from the new season, she did however, regained her major status in Season 17, and redeemed herself in the video game "South Park: The Fractured But Whole", and has remained her lovable self since season 18.)
 * Gerald Broflovski (Season 20; He becomes an unsympathetic asshole who hides being a troll to his whole family, causes the Danish to start the whole Troll-Trace program in the first place by causing Freja Ollegard to commit suicide after trolling her constantly, makes the split of the boys and girls at South Park Elementary (which also causes the boys to turn on Cartman at first), and frames Ike and Kyle for some of his actions. He doesn't even learn a lesson from any of his actions and he gets away scot-free with his trolling.)

Angry Birds Toons

 * Red (Season 2-3; He became an overprotective angry bullylike jerk that likes beating the innocent pigs for fun and leaving them to starve. He is also racist towards the pigs and is very mean to them for no real reason.)
 * Chuck (Seasons 2-3; became a annoying idiotic jerk who cares more about looking cool than protecting the eggs.)
 * Jim, Jake, And Jay, (The Blues, Seasons 2-3; They became annoying troublemaking brats that also like to beat up the pigs for fun.)
 * Matilda (Season 2-3; She became an OCD overprotective Neat Freak that wants everything to be perfect.)
 * Bomb (Seasons 2-3; He became a boring loon with no personality and eats ice cream for no reason.)
 * The Pigs (Seasons 2-3; They became 1-dimensional villain characters who want to steal the eggs from the Birds for no real reason when they could’ve eaten something else, They also became punching bags for the Birds.)

Dragon Ball

 * Son Goku (GT and Super; became dumber and more of a manchild)
 * Chi-Chi (Z, GT and Super; became an obnoxiously overbearing mother to her sons, Gohan and Goten, to the point where she attempted to take Gohan's infant daughter away from him as she couldn't stand the thought of her becoming a Z-Fighter when she grew up)
 * Broly (Z: Broly - Second Coming; became a brainless lunatic who did nothing but scream "KAKAROT!" at the top of his lungs)
 * Son Goku (Dragon Ball GT and Super; became dumber and more of a manchild)
 * Chi-Chi (Dragon Ball Z, GT and Super; became an obnoxiously overbearing mother to her sons, Gohan and Goten, to the point where she attempted to take Gohan's infant daughter away from him as she couldn't stand the thought of her becoming a Z-Fighter when she grew up)
 * Broly (Dragon Ball Z: Broly - Second Coming; became a brainless lunatic who did nothing but scream "KAKAROT!" at the top of his lungs)

Turbo F.A.S.T

 * Theo/Turbo (Turbo F.A.S.T (Season 3)) became a Gary Stu who usually cares about winning and mustaches more so than the first two seasons.
 * Skidmark (Turbo F.A.S.T (Season 3)) became crazier than he was in the first two seasons and often cares about hanging out with White Shadow, even more so than the first two seasons.
 * Burn (Turbo F.A.S.T (Season 3)) became a greedy and aggressive mean popular girl who lost all of her character development throughout the series and constantly bullies her teammates (even Chet) whenever they mess something up for her or get what she wants, sometimes if by accident and even for petty reasons.
 * White Shadow (Turbo F.A.S.T (Season 3)) became dumber than he was in the first two seasons who constantly cares about food than his other trails (e.g. Kung Fu, and racing).
 * Whiplash (Turbo F.A.S.T (Season 3)) became an even more short-tempered, loud man who often treated the other snails like slaves and also very stupid.
 * Smoove Moove (Turbo F.A.S.T (Season 3)) became a lazy slacker Butt-Monkey without any personality as his insecurities get worse, and his team does nothing to help when he gets treated like a punching bag.
 * Hardcase (Turbo F.A.S.T (Seasons 3)) became much of a filler generic doomsday villain who once nearly got everyone in Turbotown killed by the stink bomb attracted on the dryer in Turbo Does Laundry.
 * Dunce (Turbo F.A.S.T (Season 3)) became a plot device that only served as filler and to keep up with the plots in Turbo-focused episodes.
 * Mel Shellman (Turbo F.A.S.T (Season 3) became overprotective over Charlie too much to the point where he couldn't let the latter get a new best friend.

Buddy Thunderstruck

 * Buddy Thunderstruck (Get the Hock Out and Cannonballistic; became dumber and more immature than he was in the previous episodes since he usually does stupid things, often gets himself in trouble, doesn't listen to other people, and acts like he doesn't care for the bad things that happen to them or even himself to the point of him never getting told off or punished for his mean-spirited and stupid actions).
 * Artichoke (Buddy Thunderstruck in Get the Hock Out; became a stereotypical Edgelord who only threatens to kill other people when he gets distracted or someone stole his motorcycle).
 * Auntie Uncle (Buddy Thunderstruck in Get the Hock Out]; became an extremely braindead and spoiled Mary Sue-typed party animal who only cares about losing Buddy's money to other people and even sold all of Buddy's furniture and even her own furniture to Big Tex just to "keep the business going" which could give post-movie Patrick Star or modern Peter Griffin a run for their money).
 * The Townspeople of Greasepit (Buddy Thunderstruck in Get the Hock Out; most of them (expect Muncie, Mama Possum's babies, the Beavers, Big Tex, and Artichoke) either became total idiots than they were in the previous four episodes, butt-monkeys or joke fodders who never punish or call Sheriff Cannonball on Buddy and Darnell for their actions up to the point where they both get off scot-free).

Battle for Dream Island

 * Pencil (BFB) (Battle For BFDI; became a mean unlikable leader)
 * Leafy (Battle For BFDI; became a ungrateful mary sue who damages her relationship with Firey. Fortunately, Leafy apologized to Firey in BFB 22)
 * Firey (Battle For BFDI; became a selfish Gary Stu who thinks that Leafy stole Dream island, but is still well received by fans)
 * Book (Battle For BFDI; became an unlikable jerk to Taco)
 * Foldy (Battle For BFDI; became a bland Mary Sue who, in BFB 11, made Iance lose all because Stapy was eliminated)

Glee

 * Will Schuester (Glee Season 4-5); Became a stubborn, obsessive and pushy manchild.
 * Rachel Berry (Glee Season 2); Became a complete psychopath who never does something without an ulterior motive of stardom.
 * Tina Cohen-Chang (Glee Season 4-5); Became an unlikable diva.
 * Blaine Anderson (Glee Season 3-5); Became an immature manchild.
 * Sam Evans (Glee Season 4-6); Became dumb as a rock, to the point where he was barely functional.

Johnny Test

 * Johnny Test (Johnny Test; Seasons 4-6, in Seasons 1-3 he had a smoother character design, voice and was a lot more respectful towards his family including his sister, by Seasons 4-6 though he had become a lot more rude, selfish, and an overall generic protagonist.)
 * Susan and Mary Test (Johnny Test; Seasons 4-6, went from great partners in training with comedic traits and creative experiments, with safety precautions when testing on Johnny to having no problem experimenting on Johnny no matter how dangerous. More than half of those are for Gil. They are also hypocrites)
 * Bling-Bling Boy (Johnny Test; Seasons 4-6; became blander as a villain, while at the same time actually gaining character development)

Danger Mouse

 * Danger Mouse (Danger Mouse; Became a stereotypical hero who can often be very unlikable)
 * Penfold (Danger Mouse; Went from a humorous dim-witted coward to a stereotypical bland and gay coward)
 * (Danger Mouse; Season 5 (1981)-onward; Became a dumb yet likable colonel)
 * (Danger Mouse; Season 5 (1981)-onward; Went from a loyal henchman of Baron Greenback to a stupid henchman)
 * (Danger Mouse; Season 4 (1981)-Season 10 (1981); Season 1 (2015)-onward; Started off not having a problem, then started hating his job wanting to quit since the fourth seasons seventh episode Tower of Terror, saying he wanted to be on Radio 3. However, after the reboot he started tolerating his job more, being the comic relief character and a show-stealer, all while still being likable)

Be Cool Scooby Doo!

 * Fred Jones (Be Cool, Scooby-Doo!; Became even more obsessed with traps to the point it permanently damages his relationship with Daphne.)
 * Daphne Blake (BSCD; Became very stupid, to the point where it also damages her relationship with Fred.)
 * Velma Dinkley (BSCD; Became a know-it-all.)
 * Shaggy Rogers (BSCD; Also became very stupid, to the point where he is more stupid than cowardly)
 * Scooby-Doo (BSCD; Same as Shaggy)

Total Drama

 * Chris McLean (Total Drama; Total Drama: Revenge of the Island onwards; became even more psychopathic later on in the series)
 * Courtney (Total Drama, Total Drama Action onwards; became more aggressive)
 * DJ (Total Drama, Total Drama World Tour; became a crybaby who complains about an "animal curse")
 * Gwen (Total Drama, Total Drama Action onwards; she was originally a moody and sarcastic yet kindhearted girl, but in "Action", her impulsive actions between her and Trent somewhat caused her to lose Trent as a boyfriend, and in "World Tour", she became more of a jerk, and while she did show some remorse for her kissing Duncan, and when everyone finds out about the kiss, she doesn't vote herself out or apologize, and she tried to manipulate Cody's feelings to vote Courtney off, and in "All-Stars", she became more girly)
 * Duncan (Total Drama, Total Drama World Tour onwards; in "World Tour", he became more of a jerk to the point of cheating on Courtney, and in "All-Stars", his soft side gets exaggerated to the point of where he can't stop himself from being nice)
 * Lindsay (Total Drama, Total Drama All-Stars; became even more stupid to the point where she couldn't push a cart)
 * Leshawna (Total Drama, Total Drama Action onwards; in "Action", she fake-cried to her teammates about going to the spa, and proceeded to trash-talk them afterwards, and in "World Tour", she became bossier and more rude to her team)
 * Owen (Total Drama, Total Drama Action; became more unfunny and obnoxious)
 * Sierra (Total Drama, Total Drama All-Stars; became more insane and imagines Cameron as Cody)
 * Zoey (Total Drama, Total Drama All-Stars; became a Mary-Sue and became dumber to the point she didn't realize Mike was Mal)
 * (Total Drama, Total Drama All-Stars; became dumber and more incompetent, though this is a good flanderization because it made him more likable and have more funny moments)
 * Geoff (Total Drama, Total Drama Action; he became more like Chris in the aftermaths)
 * Bridgette (Total Drama, Total Drama Action onwards; became more obsessed over Geoff, and in "World Tour", she couldn't control her hormones to the point where she cheats on him with Alejandro)
 * Trent (Total Drama, Total Drama Action; became obsessed with Gwen and the number 9)
 * Ezekiel (Total Drama, Total Drama World Tour onwards; became the Gollum of the series)
 * Cameron (Total Drama, Total Drama All-Stars; became more dumber, and didn't realize Mal exists even though Cameron is supposed to be one of the smartest characters in the series.)
 * Dave (Total Drama, Total Drama: Pahkitew Island (episode 6/7-onwards), became a crybaby who was obsessed with Sky, to the point where he voted himself out in episode 9, and in the finale, he went insane and tried to hurt Sky)
 * Sky (Total Drama, Total Drama: Pahkitew Island (episodes 9-ownards), became overly competitive to the point where she threw a childish temper tantrum in the finale)
 * Cody (Total Drama, Total Drama World Tour; Became somewhat hypocritical and a jerk, though this is minor, and can be seen as good by some people)

Thomas the Tank Engine

 * Thomas the Tank Engine (Thomas & Friends; became an idiot who never pays attention and makes lots of mistakes between Seasons 12-16.)
 * Gordon the Big Engine (Thomas & Friends, Season 8-15); he was flanderized into becoming the Thomas & Friends version of Brian Griffin from Family Guy and acts like an arrogant jerk.)
 * Toby the Tram Engine (Thomas & Friends, Seasons 9-16; 2005-2012 He went from an old and wise engine into a paranoid wimp who is too scared to do anything.)
 * Edward the Blue Engine (Thomas & Friends, Seasons 11-16; Much like Toby, he went from an old and wise engine into a paranoid wimp who is too scared to do anything.)
 * Henry the Green Engine (Thomas & Friends, Seasons 12-19; He went from a kind and friendly gentle giant into a coward who constantly worries too much about every little thing and is too stupid to do anything right.)
 * Percy the Small Engine (Thomas & Friends, Seasons 15-16); Percy went from being a naive engine, into a a idiot, dimwit and a crybaby who obsesses over Thomas' attention.)
 * Emily the Stirling Engine (Thomas & Friends, Seasons 8-10, 12-16; She went from a kind and helpful engine to a bossy, naggy and selfish engine.)
 * Skarloey and Rheneas (Thomas & Friends, Seasons 9-12, They started out as kind and wise old engines into spoiled, immature brats who like to fight and argue over trains.)
 * Sir Topham Hatt(Thomas & Friends, season 12-16 (All Engines go), went from a stern but fair father figure to the engines to a goofy idiot who acts more like a comic relief.)

SuperMairoLogan

 * Mr. Goodman (SML; Went from an decent person to a money-loving, money-hungry jerk towards Mario)
 * Mario (SML; He went from a down to earth man living in a house full of idiots to a sometimes stupid yet stereotypical dad and a Butt-Monkey,but is still innocent and likable)
 * Bowser Junior (SML mid-late 2019-2020; Became extremely unlikable, overly annoying, unfunny, and dumb, and tortures Chef Pee Pee and Cody for no reason other than to entertain himself, though he is more likable in late 2020 onwards)
 * Joseph (SML 2017-2020); Became an unlikable character whose sole purpose is to be Bowser Junior's annoying Yes-Man, try to look cool and to be on the radical side of things (even if it is genuinely dangerous and questionable), and also became a greedy spoiled jerk on par with The Goodman Family in "Joseph the Millionaire!".
 * Rosalina (SML 2016-2017 & 2019-2020; Became an insensitive, excessively dull-witted, and nagging mother who yells at Mario and defends Jeffy for no good reason. Not even she was immune to Flanderization while she was the typical dumb blonde character as well)

Inanimate Insanity

 * Paintbrush (Inanimate Insanity Season 2; went from a responsible contestant who is pragmatic in their approach to challenges and life to an overly competitive, impatient, bossy, and short tempered jerk who often takes things WAY too seriously. The way they treat Fan in episodes like Mazed and Confused and the second part of Kick the Bucket also possibly hints that they often overwork any member of the Bright Lights whenever they slack off)
 * Nickel (Inanimate Insanity II; went from a critical character to a selfish and egoistical jerk that made Suitcase paranoid and tried to break up Suitcase and Balloon)

Cailliu Gets Grounded

 * Caillou (Caillou Gets Grounded; became an extremely unlikable, mean-spirited, callous, sociopathic and malicious jerk who takes pleasure in constantly causing trouble for no reason and making his family's and other's lives miserable. True, he was unlikable in the original PBS series because he was very bratty and often threw temper tantrums. However, he was nowhere near as unlikable as he is here. In fact, he is so unlikable in this series that he could give his original PBS counterpart a run for his money. However, his personality can sometimes vary since there is more than one user who makes the videos.)
 * Boris and Doris (Caillou Gets Grounded; became cruel and abusive parents towards Caillou who constantly ground him for ridiculously long periods of time for his bad behavior and sometimes even ground him for stupid and nonsensical reasons or for things that aren't that big a deal. They are especially abusive towards Caillou in the Punishment Day Videos because they give him over-the-top punishments. In fact, they can be just as bad as, if not sometimes even worse than Caillou. However, Doris is shown to be somewhat more caring towards Caillou than Boris. Boris also finds enjoyment of torturing his son for fun. They also abuse Caillou instead of punishing him. Doris even defended him on some occasions. Like Caillou, their personalities can sometimes vary since there is more than one user who makes the videos.)
 * Rosie (Caillou Gets Grounded; became a huge tattletale, Caillou's punching bag and a Mary Sue, although she is still a likable character compared to Caillou, Boris, Doris and the following two characters in Caillou Gets Grounded, which are Miss Martin and Dora. However, she can have some unlikability at times, such as by contributing to Caillou's over-the-top punishments in some of the Punishment Day Videos. Like Caillou, Boris and Doris, her personality can sometimes vary since there is more than one user who makes the videos.)
 * Miss Martin (Caillou Gets Grounded; became a stereotypical mean teacher towards Caillou who treats him in a similar way to how Boris and Doris treat him, except she is not his parent and she does not ground him. Like Caillou, Boris, Doris and Rosie, her personality can sometimes vary since there is more than one user who makes the videos. The only thing about her that's better than her original counterpart is her character design. Still, this does not excuse her flanderized personality.)
 * Dora (Caillou Gets Grounded; is the same as Caillou, except she was likable in the original Nick Jr. series and its sequel Dora and Friends: Into the City!. Like Caillou, Boris, Doris, Rosie and Miss Martin, her personality can sometimes vary since there is more than one user who makes the videos.)

SMG4

 * Bob Bobowski (SMG4 2018); (although he was always obnoxious, but they were done in a hilarious way, however in 2018, he became more unlikable where in "Mario and the T-Pose Virus", he got his friends turned into T-Pose Zombies, and in the "The Rapper Bob Arc", he made a nasty speech to Boopkins to the point where he made him cry, and in the same arc he became more of a jerk to the point of dissing his friends in a rap just to become more famous)
 * Axol (SMG4 late 2020-onwards); (he went from a kind and understanding manga artist to a simp who lusts over Melony no matter what)
 * SMG4 (SMG4 2017-onwards); (he went from being the straight-man with Mario's stupidity to becoming a stereotypical meme-loving addict)
 * Princess Peach (SMG4 2018-onwards); (she became much more bossy, rude, and selfish than her previous personality to the point where in "If Mario was In.. Fall Guys", she punished Mario after Mario gave King Bert, the original owner, the crown instead of her. This showed that she cared about herself, also in "Food Wars", she threatened to kill Mario and his friends for participating at the "party")
 * Toad (SMG4 season 2014-2015 & 2018-onwards)(he received two flanderizations; In the first three years, he went from a comedic, mistreated and a slightly grumpy and sarcastic helper, similar to Squidward Tentacles in Seasons 1-4 and Season 9-present of SpongeBob SquarePants. However, in 2014-2015 he became a crazily obsessed fan of Mario who is addicted to sugar and often played as a poor attempt at comic relief; a complete 180 from his original personality. He would later retain his original personality in the later years, but in 2018-present, he would later become a more grumpy person who would often serve as a punching bag who is heavily mistreated by Toadette (similar to Squidward in seasons 5-8 of SpongeBob SquarePants) to the point of being more mean-spirited than funny)
 * Bowser (SMG4 seasons 2014-2015)(he used to be a misunderstood villain of the series who was insecure on the inside. In seasons 4-5, he became a moronic comic-relief who is obsessed with "swag" and "being fabulous" (an easy example of this is in the 2014 episode, "SwagQuest", where he's overly obsessed with making Luigi hip for a swag party at Peach's Castle). Similar to Toad's 2014-2015 flanderization, this is typically played as a cheap attempt at comedy.)
 * Fishy Boopkins (SMG4 mid 2017-present) (he essentially became an anime-obsessed weaboo who in almost, if not every, episode he appears in, he mentions anime or anything related to that)

Miscellaneous

 * Harry Potter (Harry Potter novels 5-7; became an unlikable jerk. However, it is justified, as it was actually a result of trauma caused by Cedric Diggory's death.)
 * Hermione Granger (Harry Potter novels 5-7; became an annoying Mary-Sue and as much of a jerk as Harry, albeit it is a result of the puberty)
 * Ellie (The Last of Us Part II; She went from being a caring, yet devious little girl, to an overall cold-hearted person, who goes throughout the whole game assaulting random people who she comes across)
 * Stan Smith (American Dad!; Season 11-present; went from being a well-meaning father, into the American Dad version of Peter Griffin).
 * Roger Smith (American Dad!; Season 8-Present; went from being a hilarious into a sadistic character who enjoys murdering.
 * Superboy-Prime (Infinite Crisis); became an angry fanboy because his version of Earth was destroyed.
 * Hank Hill (King of the Hill; is known for preferring traditional things over trendy new ones. This starts to get overdone in the later seasons; case in point, "Get Your Freak Off". In this episode, Hank is more Amish than the Amish; he's almost medieval)
 * The Annoying Orange (The High Fructose Adventures of Annoying Orange; became more annoying than he was in the web series to the point where he is not even funny)
 * oo (Foster's Home for Imaginary Friends; started out as being protective over and caring of Mac in the pilot whilst being only slightly mischievous and then became a "jerk with a heart of gold" type of character in the first season, but then eventually he lost the "heart of gold" part and just became a full-blown, straight-up, outright meanie whose jerkiness kept getting worse and worse as the show went on until he finally started leveling off around the end of the series)
 * Earl Devereaux (Cloudy with a Chance of Meatballs; became a rude and manipulative jerk in the TV show adaption)
 * Mater (Cars; became an idiot jerk in the second film, until his flandzerization is undone in Cars 3)
 * Optimus Prime (Became a psychotic killing machine in Transformers 2: Revenge of the Fallen)
 * Ren Hoek (Ren and Stimpy: Adult Party Cartoon; same as Optimus Prime)
 * Miho Nosaka (Yu-Gi-Oh! 1998; became a selfish, hypocritical ditz who uncaringly strings Honda around when she clearly has no interest in him and just uses him for her own personal gain)
 * Sakura Haruno (Naruto; became a violent psychopath who often attacks Naruto for the smallest infractions or even for no apparent reason)
 * Sheen Estevez (Planet Sheen; Went from being a funny comic relief to an immature, childish, and unfunny idiot)
 * Spike Bulldog (The Tom and Jerry Show; went from being a friend to Jerry in the original, theatrical shorts to a mean-spirited, short-tempered jerk who hates and bullies both Tom and Jerry)
 * Tommy Oliver (Power Rangers; became an annoying Ranger every season after season)
 * Manny the Mammoth (Ice Age; became a stereotypical over-caring father in Ice Age 4: Continental Drift and became dumber and dumber as films went on.)
 * Sid the Sloth (Ice Age; Became a stereotypical lazy bum in Ice Age 4: Continental Drift and became dumber and dumber as films went on.)
 * Jungho (The Devil's Boy; Season 2-3); Became a more psychotic, unheroic, vengeful bullied boy after her crush, Lee Yoonhee commited suicide.
 * John Doe (UnOrdinary; 2nd half of Season 1, Season 2); Became an arrogant, unheroic bullied teenager, who grew tired of being crippled by his tormentors.
 * Dongtae (DICE: The Dice That Changes Everything; season 4)
 * Lego (Object Invasion; Episode 6-onward; he went from a kind, yet self conscious friend of Cup to a bossy leader who gets angry when his team loses, and he once blamed his own team for losing the challenge, and doesn't care about whatever gets in his way, which led to his elimination)
 * Greg Heffley (Diary of a Wimpy Kid: The Long Haul (film) became an idiot.
 * Frank Heffley (Diary of a Wimpy Kid: The Long Haul (film) is the same as Greg.
 * Susan Heffley (Diary of a Wimpy Kid: The Long Haul (film) became a selfish and egotistical mother who belittles her family and bashes modern technology. She can also be an idiot at times like Greg and Frank.
 * Andy Bernard (The Office (US): Seasons 8 and 9; became very annoying.)
 * Puckett (iCarly Seasons 4-5; Sam & Cat); Was flanderized twice (first one was good, second one was bad). In the earlier seasons of iCarly, she started out as being an aggressive tomboy. During Seasons 4-5, however, she became somewhat less aggressive and more girly (this was good Flanderization that made her more lovable and memorable). Then, during Sam & Cat, she became a selfish jerk (which unfortunately, was a bad flanderization rather than a good one).
 * Cat Valentine (Victorious Post Season 2, Sam & Cat) became even dumber than she was in the first 2 seasons of Victorious to the point of being an absolute idiot.
 * Sam Wilson/Falcon (Marvel Comics; became out of character after becoming the "new" Captain America)
 * Mark Taylor (Home Improvement; Season 7; became a gothic weirdo.)
 * Agent 3 (Splatoon); Started out as the hero you play who defeated Octarains because they stole the Great Zapfish, to a heartless racist jerk who attacked Agent 8 simply because he/she was an Octoling and Octolings used to be the bad guys in Splatoon, even though this Octoling became good due to hearing the Calamari Inkantation and wouldn't attack Agent 3, yet Agent 3 still wants to attack Agent 8 because they were an "evil" Octoling. Thankfully, Agent 3 became good in Octo Expansion because he/she saved Agent 8 and Cap'n Cuttlefish from being blended alive and was nice to Agent 8 and realized that not all Octolings are bad guys.)
 * Wonder Woman (2011); Became a selfish, cold-hearted and murderous bully.
 * Superman (DCEU); Became an eternally depressed grump who almost never smiles and a boring Jesus allegory.
 * Lex Luthor (DC Extended Universe); Became a spoiled daddy’s boy who acts like a wacky cartoon character.
 * Joker (DC Extended Universe); Become a generic edgy gangster wannabe with tattoos and silver teeth.
 * Lois Lane (DC Super Hero Girls (2019)); Became a manipulating freak and Mary Sue clone of Courtney who once followed the Superhero Girls around to prevent them from protecting Metropolis from the Killer Moths, resulting in the city being attacked by them.)
 * Luke Skywalker (Star Wars: The Last Jedi); became a cowardly old grump who nearly refused to train Rey.
 * Blossom, Bubbles, and Buttercup (The Powerpuff Girls (2016)); (Blossom became a neurotic geek, Bubbles became one of the girliest girls while still retaining some of her more psychotic episodes, and Buttercup became a bully).
 * Jerry (Gene Deitch Version); Went from being a troublesome and cunning, but cute, funny, and loveable mouse to a flat-out sadistic jerk who enjoys torturing Tom for fun and even makes Tom's owner torture him even more. Luckily, he redeemed himself in the Chuck Jones-era.
 * Daffy Duck (DePatie Freleng/Seven-Arts era); went from a mischevious screwball prankster into a grouchy, humorless sadist who heavily disregards others in favor of getting what he wants and inflicts abuse on innocent characters such as Speedy Gonzales).
 * Eustace Bagge (Courage the Cowardly Dog in Ball of Revenge); Became a murderous jerk who wants Courage dead because he gets all the attention from Muriel.
 * Daenerys Targaryen (Game of Thrones Season 8 Part 2; Became a poorly written mad tyrant.)
 * Junko Enoshima (Danganronpa 3: The End of Hope's Peak High School; Became an incompetent, one-note "I'm going to destroy civilization because I'm evil!" Generic doomsday villain.)
 * Pac-Man (Pac-Man and the Ghostly Adventures; Went from a video game icon who turns out to be lovable towards many gamers into a glutton who focuses more on food rather than helping others.)
 * Earthworm Jim; Was a hilarious and memorable video game character who turned out to be quite lovable from the cartoon and towards many gamers because of the first two games, but Earthworm Jim 3D made him somewhat annoying, forgettable, and unfairly accident-prone.
 * Tyler Navarro ("Power Rangers Dino (Super) Charge"; became an idiot, an unlikable Red Ranger and one of the most annoying characters)
 * Riley Griffin ("Power Rangers Dino (Super) Charge"; became immature and only cares about winning.)
 * Koda ("Power Rangers Dino (Super) Charge"; became a silly comic relief in the second season)
 * Woody Woodpecker (Woody Woodpecker 2017; Became an unlikable sadist)
 * The Banana Splits (The Banana Splits Movie; Became murderous monsters)
 * Lanolin (Orson's Farm; Became a HUGE jerk towards everyone, especially Roy)
 * Wreck-It Ralph (Ralph Breaks the Internet; became an immature and selfish jerk who lives to only have Vanellope by his side, even though he redeems himself towards the end)
 * Vanellope von Schweetz (Ralph Breaks the Internet; She has become extremely selfish and makes many callous and irresponsible decisions)
 * Mushu (Mulan II; went from a funny comic relief to a self centered jerk for no reason.)
 * Hua Mulan (Mulan (2020); became a Mary Sue and physical fighter and was apparently born gifted.)
 * Kai (LEGO Ninjago: Masters of Spinjitsu; Seasons 8-12, went from a short-tempered, yet caring ninja to a whiny, narcissistic character.)
 * Jay (LEGO Ninjago: Masters of Spinjitzu; Seasons 8-onward; His timidness overtime evolved into just being utterly dim-witted)
 * Jeffy (SML 2016-now); While he was stupid & mostly annoying ever since his introduction into the SuperMarioLogan series, he has now become dumber, controversial & imbecilic for infamous reasons, manipulative at times, has become more of a cash cow for SML now, and he has also become a lot more obnoxious with his tediously excessive jokes being more exaggerated than before (so much that it makes Bowser Jr look harmless by comparison in some instances), and such to the point that there were some fans that wanted Logan to burn the Jeffy puppet.
 * Lloyd Montgomery Garmadon (LEGO Ninjago: Masters of Spinjitzu; Seasons 11-present; became more of a stereotypical leader in a kids' cartoon.)
 * Dareth (LEGO Ninjago: Masters of Spinjitzu; Seasons 8-present; became more of an attempted comic relief character than an actual comic relief character)
 * Jack Sullivan (The Last Kids on Earth; Became an unlikable idiot)
 * Mrs Axzyte (Axzyte; Went from a mother who disliked games into an abusive mother)
 * The Days Union (ROBLOX; Went from being passive myths that are against The Night Coalition to being hostile and rabid myths)
 * JackCult (ROBLOX; Same as The Days Union, he went from a nice 14 year old child that was the only safe Cult Family myth to a hostile myth)
 * BrandonCult (ROBLOX; Went from a serious myth from a corrupt family to a user that looks unrecognizable and acts nothing like his past self, and also made a disgusting game where you literally eat poop.
 * Norman Price (Fireman Sam Season 6-Present; He went from a mischievous boy who likes to play tricks to a whiny, annoying brat who does horrible things for the pettiest reasons)
 * Elvis Cridlington (Fireman Sam Season 6-Present; He went from a not so bright but friendly firefighter to an incompetent idiot)
 * Scoop (Bob The Builder (2015 Reboot); He went from a sensible and reliable leader to a clumsy and careless goofball who messes everything up)
 * Lofty (Bob The Builder (2015 Reboot); He went from a friendly, shy coward to a sarcastic, cynical, intelligent crane who isn’t scared of anything anymore)
 * Muck (Bob The Builder (2015 Reboot); He went from being a funny but reliable vehicle, into an idiot who screws up like Scoop).
 * Tiny Kong (Donkey Kong; She went from a tough, small, and cute little girl who was able to shrink (hence her name), to a tall, sexual teenager, who has no personality.)
 * Lincoln Loud (The Loud House Season 4-Onwards; He became even more of a butt monkey and also became more selfish.)
 * Leni Loud (The Loud House; Became even dumber to the point she went to pre-school in Schooled.)
 * Baby Bop and BJ (Barney & Friends; in later seasons, Baby Bop can no longer count and the two constantly need help from Barney to learn)
 * Natsuki (DDLC: Loser MC; Became even more mean to MC)
 * Shadow The Hedgehog (Sonic Boom; went from a likable Anti-Hero to an unlikeable villain with no backstory)
 * Knuckles The Echidna (Sonic Boom; becomes an idiot tough guy)
 * Michelangelo (Teenage Mutant Ninja Turtles 2012; became even more of an annoying idiot in Season 5).
 * Big Bird (Sesame Street; Journey to Ernie made him a Steve Burns-like host)
 * Zoe (Sesame Street; became obsessed with ballet)
 * Blue (Blue's Clues; Blue's Room made her an annoying, overly-talkative dog)
 * Cookie Monster (Sesame Street; became an omnivore)
 * Yoshi (Yoshi Topsy-Turvy; lost his ability to make and throw eggs)
 * Sanji (One Piece, Went from a really cool guy who had a weakness for women into a perverted guy who always goes blood-losing every time he sees a girl)
 * Makoto Itou (School Days and Summer/Shiny Days, a cute shy guy who become an irredeemable jerk and a sexual predator.)
 * Johnny Bravo (Season 2-3) (Johnny Bravo, became as dumb as a bag of rocks.)
 * Silver The Hedgehog (Sonic: Super Genesis Wave; became a cruel jerk to Sonic and everyone.)
 * The Cat in the Hat (The Wubbulous World of Dr. Seuss; started out as a trickster, but in Season 2 he became more of a Bear in the Big Blue House-like host who, like Elmo from Sesame Street, gets way too much screen time)
 * Jenna (30 Rock; became an attention whore and a self-centered diva in Season 3)
 * Eric Matthews (Boy Meets World; became dumber and dumber as the show went on starting in Season 3 to the point where he was unable to put the right shoes on his feet)
 * Simba (The Lion Guard; A likeable and sympathetic hero who became an unlikeable and stereotypical overprotective and over-caring father towards both Kion and Kiara.)
 * Kiara (The Lion Guard; Became an arrogant and snobby brat.)
 * Nana (Elfen Lied; rather than improving to protect her family & friends, she becomes more of a pathetic damsel fighter in many later parts of the manga, where Kurama or Bando always save her & Mayu.)
 * Edward Elric (Fullmetal Alchemist (2017 film); becomes a pathetic stereotypical shounen anime protagonist who lacks the charm of the original Edward Elric)
 * Winry Rockbell (Fullmetal Alchemist (2017 film); she is turned into a stereotypical whiny damsel in distress who always needs saving from Edward Elric)
 * Jimmy (Jimmy Two-Shoes Season 2); became more of an idiot.
 * Duela Dent (The New 52; became an edgy flesh-face wearing sociopath)
 * Heloise (Jimmy Two-Shoes; Became a punching bag)
 * Reginald "Shark" Kastle (Yu-GI-Oh! Zexal) became a stereotypical emo and bland tyrant who is revealed to be a Barian Emperor named Nash, and thinks Yuma and the others are not his friends.
 * Rio Kastle (Yu-GI-Oh! Zexal) became a bland remorseless girl who is revealed to be a Barian Emperor named Marin, and thinks Yuma and the others are not her friends.
 * Aster Phoenix (Yu-GI-Oh! Arc-V) became a ruthless individual who thinks hurting people in dueling is wrong from Leo Akaba.
 * Banjo (Banjo-Kazooie Nuts & Bolts) got flanderized literally into a lazy bear. Sure, the sequels before Nuts & Bolts did show Banjo's lazier side, but Nuts & Bolts did it a lot worse than before to the point that he can't do anything himself thus being an obstruction to Kazooie.
 * Picard (Star Trek: Picard) became a senile anti-male privilege caricature instead of a selfless hero in the TNG.
 * Angela (mh:besttvshows:Talking Tom & Friends) she has suffered from four flanderizations, two of which are good and the other two which are bad. She was unlikable in the first season, as she was often rude to Tom and sometimes the others as well, but she became even worse in the second season. She improved in the third season, went back to being bad in the fourth season and returned to being good in the fifth season.
 * Jewel (Rio 2) became an abusive, toxic wife who takes control of every decision.

The Overall Reason Why This Trope Sucks

 * 1) Basically, this trope serves as reverse character development, where the characters you love become more unlikeable.