Ant-Man: Hank Pym has suffered from this perhaps more than any other Marvel character. During a single incident in which he was suffering a nervous breakdown and had just completed building a robot programmed to kill all of his friends, Hank struck his wife, Janet Van Dyne (The Wasp). This immediately had the effect of establishing him in canon both as a wife-beater and severely mentally ill. Dozens of writers over the years have gone back to this time and again, with at least three different stories having been told about the two of them coming to terms with what happened. Hank's remorse is so Flanderized and extreme that he called himself the Wasp when she was thought to be dead.
This carries over even to an alternate version of the character. The Ultimate Universe version of Pym was written as a cruel sadist who tortures his wife nearly to death and stole all of his ideas from her.
As of Secret Empire, Hank (after having merged with Ultron) finally snaps and calls out the then 'Captain HYDRA' Steve and the AI version of Tony Stark for all the stuff that they've pulled which, especially in Tony's case (Steve was morally flipped against his will), makes the incident with Janet, awful as it was, look like a playground scuffle. He has a point, unfortunately.
Captain Marvel: Carol Danvers aka Ms. Marvel/Captain Marvel has had her furious impatience and Control Freak qualities shoot through the roof. Originally she was abrasive at worst and most of her anger and outbursts were sympathetic, from having to deal with the very sexist J.Jonah when she worked temporarily as his magazine editor to giving the Avengers a collective What the Hell, Hero? over their nonchalant reaction to her getting mystically raped and impregnated by her son Marcus. Modern comics namely the ones after Carol took the Captain Marvel mantle have exaggerated Carol’s worst traits to ludicrous levels to the extent she makes even Tony look reasonable in comparison cumulating in Civil War II where calling her a Villain Protagonist is putting it mildly and even Maria Hill tells her she’s getting out of control. There’s also her hatred of her rival Rogue which went from off as understandable anger to “I will kick the crap out of skunk hair on sight” and in one What If? Carol literally goes across the multiverse killing every version of Rogue she can find which is kinda Disproportionate Retribution for throwing someone off a bridge one time. Thankfully writers did eventually settle on Carol forgiving and befriending Rogue which is more that can be said about the rest of her problems.
One element of Carol’s character that’s long been subject to flanderization is her ass, particularly in her Ms Marvel leotard (which Carol herself created and admiredherself in). Originally her leotard covered her butt and if anything it was tamer than her first outfit which displayed her navel. Eventually artists got hornier and Carol’s well formed cheeks were larger and on nigh-constant display to point of In-Universeworship despite Carol once remarking how the outfit gives her the worst wedgie imaginable. Once she became Captain Marvel this became more toned down barring a few artists.
Johnny Storm started off as a somewhat-conceited daredevil hero of the teamnote It's been joked that while the battle cry of the Avengers is "Avengers assemble!", that of the Fantastic Four is arguably "Johnny, wait!". Since the eighties, he's become increasingly more stupid and narcissistic, to the point where he now appears to be a ditzy, Ambiguously Gay metrosexual completely in love with himself.
Reed Richards was originally a tad eccentric and rather emotionally stunted, but was Flanderized in the late 1990s/2000s into a borderline savant who doesn't understand human social behavior. This pretty much is part and parcel of Reed's slow derailment from a many-layered, infamously trope-defying character into a generic scientific supergenius strawman. Perhaps most tellingly, Reed was originally written as a veteran of World War II before Comic-Book Time forced the writers to cut that detail from his backstory. After 40 years of intense Flanderization, though, it's practically unthinkable that the current comics' pencil-necked nerd would have ever even considered serving in the Army, let alone that he would ever have fought in Nazi-occupied France in the Big One.
Inverted with The Thing: in his earliest appearances, he was a complete jerkass who was constantly picking fights with not only Johnny, but Reed, and had no use for people whom he felt were judging him. Later on, he was portrayed as more of a tough guy with a heart of gold.
Subverted with Sue Storm, who was originally called the Invisible Girl, and useless in a fight. She gained the ability to create force-fields, became a more competent fighter, took on the name Invisible Woman (after all, Iceman and Spider-Man were supposed to be teenagers but never referred to as "boys") and has sometimes served as a more competent leader especially during such time as Reed was away.
The Incredible Hulk: The Hulk's raw power has been greatly exaggerated. In his first appearance, Hulk was perfectly capable of fluent speech and clear-minded reasoning. Over the years the "dumb" part of Dumb Muscle got amplified along with the "muscle", until we reach the iconic "HULK SMASH!" levels. Then, Peter David got the idea of explaining this as two different facets of Bruce Banner's fractured mind manifesting in different types of Hulk. How his level of strength tends to be inversely proportional to his intelligence has been explained by that his ability to reason tends to put limits to how much pure rage he can build up. An alternate universe supervillain, the Maestro, was even created out of the idea of "what if the Hulk stopped caring about holding back, then lived for a hundred years?"
Contemporary Marvel writers have some fun with this when time-travel shenanigans bring later characters in contact with early Silver Age Hulk. Heroes (and villains) expecting the monosyllabic rage-monster are shocked to meet a gruff, clever Hulk who is functionally equivalent to a stronger, tougher, more devious Ben Grimm.
Hulk’s alter ego Bruce Banner’s alienating personality flaws and self-loathing have completely ballooned and have become something far more tragically twisted than originally devised. In the Silver Age Bruce was a pure Nice Guy hit with a freakish turn of fate that he has to now live with but otherwise conducted himself in a reasonably healthy manner while trying to deal with the fact he could end up Hulking Out and harming people. Later comics however started making Bruce a Darker and Edgier character who’s had demons since the moment he was born thanks to his retroactively established Dark and Troubled Past having a monstrous bastard of a father who killed his mother, resulting in Bruce having violence and rage inside him long before Hulk was “born”. One flashback arc reveals he almost bombed his own high-school as a result of bullying and in the present Doctor Doom reveals Bruce needs Hulk to vent his darker impulses.
Thunderbolt Ross aka Red Hulk, Hulk’s perpetual thorn in the side actually got his despicable tendencies flanderized over the years. While still a General Ripper, Ross was originally fulfilled a similar to role to Hulk as J.Jonah Jameson to Spidey in other words he was a constant overbearing antagonistic figure whom the hero had to live with in his dual identity but he wasn’t any more villainous than the Monster of the Week and had affable and entertaining traits. He once mused ironically the Hulk would be a better man for Betty than pencil pushing scientist Bruce. After Hulk’s identity is revealed however Ross became more and more of a colossal douchebag willingly to do anything to kill Bruce, even storm his daughter’s wedding armed with a gun. Add to that becoming Red Hulk which Depending on the Writer actually made Ross more heroic or just as commonly flanderized his hypocrisy and jerkassery even further.
Iron Man: Iron Man used to be a fairly well-rounded character, being not only a super hero, but also a captain of industry, a millionaire playboy, a bit of a womanizer, a technological genius and - rather uniquely - physically crippled from his inception. He also had a bout with alcoholism. During Civil War (2006), he got flanderized into a stubborn pseudo-fascist who'd just as soon throw his best friends in jail if they did not fall in line with the Super Human Registration Act. He had not nearly recovered from the fan-impact of that when Matt Fraction took him on an entirely different flanderization trip by reducing all his issues to side effects of alcoholism, but at least he made him be sorry for his behaviour during Civil War. Now, it seems Tony Stark spends approximately half the time agonizing about how badly he sucks. His characterization later got better during Kieron Gillen's run as Iron Man took some days off and went to a vacation in space, as has taken a more carefree approach to his life. Also, like Bruce Wayne in the DCU, Tony Stark seems to have gone from "guy with a few million bucks" to "probably the richest man in the Marvel Universe".
Even Tony’s extreme womanising Handsome Lech traits are actually Newer Than They Think. A common theme of Tony’s original comics were his reticence and fear of forming a romantic relationship with any woman due to the fact with shrapnel imbedded in his chest he could die at any moment. Once the shrapnel was removed this Celibate Hero side was royally kicked out the door and Tony started pretty much shagging his way through the Action Girl population of the Marvel universe having had relationships with Black Widow, Madame Masque, Pepper Potts, She-Hulk, Gamora (yes both green ladies), The Wasp and more recently Emma Frost in a Marriage of Convenience.
In the second series, Nico Minoru struggled to adjust to leadership, and the stress of trying to lead a team that had deliberately been designed to be dysfunctional caused her to do rash things like kiss Chase or make a deal with her evil ancestor to gain more control over her powers. When the third series came around, the writers made her increasingly Machiavellian, willing to use magic on her own teammates to control them. On the other hand, after Avengers Arena, in which Nico lost her arm and developed PTSD, writers began moving in the opposite direction, with her constantly doubting herself.
In the first two series, Molly was childish, as one might expect from an 11-year-old, but also intelligent, often managing to outwit other people. Around the time of the third series, the "intelligent" part went away and she simply became childish.
Klara's unfamiliarity with modern culture has been exaggerated to the point where she once mistook Tigra for a prostitute. Over the years, she has also gradually transformed from a mostly-sane little girl who had trouble reconciling her religious beliefs with the reality of her life to a dangerously mentally-ill Creepy Child.
She-Hulk: She-Hulk’s Really Gets Around behaviour as a beloved and lusted after Sex GodMs. Fanservice is a case of this and fairly at odds with the original conceit of her character. To wit, she was a Spear Counterpart to her cousin Bruce in not just being a Hulk but was feared the same as him and likewise had limited speech. Also while her Hulk form was undeniably more attractive than Bruce’s, the idea that she would become lusted after seemed implausible given most men were frightened of her early on (with a few exceptions like Zapper and Spider-Man). After it was established she was more intelligent than Bruce in her Hulk form she started getting written to be more flirtatious with Jen embracing her She-Hulk persona as an improvement on her mousey human self, then John Byrne got his mitts on her and Shulkie soon became the overtly fanservicey and humorous Amazonian BeautyDude Magnet. Her sexual appetite too got increasingly more and more flanderized with Jen sleeping with dozens upon dozens of dudes with the breaking point for readers being The Juggernaut for which Jen would Never Live It Down (though it was retconned to be her very open minded Alternate Self who slept with him). Worth noting this isn’t a 100% bad direction for her character and it did at least make her iconic and more well known than she would be otherwise. In fact when Jason Aaron indulged in some Revisiting the Roots when it came to She-Hulk making her more monstrous again, the outcry from fans was immense and didn’t simmer down until Jen eventually got her popular intelligent and sexy form back.
Norman Osborn started off as a corrupt businessman who had a loving, but strained relationship with his son; he had one of his colleagues arrested with fake charges and he genuinely thought giving Harry expensive stuff was enough to keep him happy. Even his motive as the Goblin was simple: he wanted to become a crime boss to see if he could, which later warped into a desire to kill Spider-Man for always stopping him. When Spidey found out who the Goblin was, he asked Norman if Harry would be proud of him, which caused Norman to lose his composure and led to his defeat and amnesia. When Harry's depression led to his famous drug problem, Norman's inability to understand his son led him to believe Harry's friends were behind it, which caused a panic attack powerful enough to bring back his memories of the goblin — every time he thought about Harry suffering, he himself suffered a mental breakdown. Then Norman died, and was brought back decades later. During this time he was supposedly a crime boss in Europe, was the mastermind behind The Clone Saga and had developed a dislike for his son, to the point he was willing to kill him without any real reason to do so. Nowadays his villainy consists of trying to take over the world, mass murder, spreading the goblin formula through manhattan to cause chaos, and has even been bonded with Carnage and plastic surgery has turned his face into a mess. He is also implied to hate every minority — most famously women — under the sun, and it's even been noted that Norman Osborn is now worse than the Goblin ever was.
Depending on the Writer, J. Jonah Jameson can suffer this. He's usually depicted as being a good man beneath his abrasiveness, and outside of his hatred for Spider-Man is an ethical journalist who crusades against injustice. Second comics just depict him as a straight-up Jerkass with none of this nuance and has no real motivation besides his hatred for Spider-Man.
The Lizard started off as an intelligent and even eloquent Mad Scientist who wanted to transform everyone into creatures like him, and had grandiose goals of world domination. Over time he degenerated into a feral, mindless beast, and became increasingly depraved as well to the point of murdering his Helpless Good Side Curt Connors's family, who he previously sincerely cared about.
The Rhino was, in his debut, a Genius Bruiser who wanted to Take Over the World. He was very quickly turned into a Dumb Muscle who generally worked as a hired goon. In recent years, this was reversed somewhat, and he developed into more of a Punch-Clock Villain of average intelligence.
The Ultimates has been criticized for being an extreme Flanderization of the Avengers. In their initial run, Mark Millar tended to take the most famous aspects of each Avenger — Captain America being of the '40s, Iron Man's hedonism, Ant-Man slapping the Wasp, The Wasp being slapped by Ant-Man, the Hulk's rage, etc. — and amplified them all several times over: Cap was painfully old-fashioned in speech and social views, Tony was always drinking and/or flirting with some blonde, Pym was a textbook wife-beater, Jan was a textbook battered wife, and Hulk was a murdering cannibal. This went into overdrive when Jeph Loeb took over the third volume. Tony was always in a drunken stupor and Cap spontaneously picked fights over Wanda's choice of attire.
Venom: The Venom symbiotes that most often show up in connection to Spider-Man have been established as having a vulnerability to fire and sonic attacks. When the latter was first used, it required a sonic emitter built by Reed Richards for this specific purpose. Over time this vulnerability has been exaggerated to the point that any loud noise can repel a symbiote. As for fire, at its worst the mere presence of a single lit lighter has been able to drive a symbiote away.
Even his powers became flanderized. At first, the idea behind his "quick healing factor" (note the word "quick") seemed to be that he simply healed faster than normal people. By some point, it was decreed that he could regenerate from a single-celled organism and was basically unkillable and therefore immortal.
Under writer Jason Aaron, another example has occurred. While Logan always had kind of a rivalry with Cyclops, the two are friends and can agree on some things, and Logan does respect Scott. Furthermore, while Logan is a Jerkass, he's willing to admit when he's wrong. Under the aforementioned writer, Logan's Jerkass tendencies have become his dominant trait, with him mouthing off about why Cyke sucks literally every time the two meet, and he outright ignores anything good the guy does.
Mystique believe it or not was (under Claremont’s pen) once upon time a more rounded villain and not the shittiest mother ever put to comic print. In Raven’s early days while still a villain she was composed, rational and pragmatic as the leader of the Brotherhood of Mutants. She also genuinely loved Rogue and wouldn’t think of hurting her and even her attitude to her son Nightcrawler while less caring was significant enough for her to hesitate from killing him in a crucial moment. She certainly had her Control Freak and jerkass villain flaws but they weren’t as prominent. After Claremont left Mystique‘s psychotic traits became far more pronounced to Carnage or Sabretooth levels and she started going to the Wu Zetian school of motherhood treating Nightcrawler and especially Rogue like absolute dirt with near constant abuse. Even Raven’s anti-human pro-human agenda can come off as Early Instalment Weirdness when reconciling it with her general Chronic Backstabbing Disorder characterisation where she’s a Boomerang Bigot who only cares about herself and Destiny. It’s taken a conservative effort from writers to dial Mystique back to just merely bad rather than an outright sadist.
Surge, whose Jerkass tendencies have been blown way out of proportion. While she was initially depicted as being kind of a Jerkass, it's understandable (she was disowned by her father for being a mutant and was a bum who had to take drugs to sort of control her powers), she was always more of a Jerk with a Heart of Gold and she was always kind to those she considered friends. While she was always an outspoken, rebellious smart ass, her later depictions make her much harder to sympathize with as she has been portrayed as an unrelenting bitch and it has become her most dominant characteristic. She has since entered Comic-Book Limbo, though her brief appearance in Avengers Academy had her being more reasonable, and had her revert to her old portrayal of Jerk with a Heart of Gold.
Mojo was introduced in a miniseries as a psychotic Eldritch Abomination obsessed whose very presence actually caused living things to wither and die and who casually committed Mind Rape. He also commissioned genetically engineered slaves to act in movies to entertain him. Even Doctor Strange feared what would happen if he stayed on Earth for long. As soon as he was brought into the main X-Men comics, the mystical powers and murderous demeanor were downplayed and the media obsession was turned up to eleven, so Mojo immediately became a comedic villain used to spoof the entertainment industry. He's still pretty damn horrible, though, and his comedic personality makes it worse when he does something like torturing Nocturne For the Evulz, or cheerfully sending someone to have their spine freaking removed.
Wolverine's daughter/sister/Opposite-Sex Clone, X-23 suffers from much of the same treatment as he does. Once her backstory was revealed, Laura was established as a highly-skilled fighter, and a very intelligent and highly educated young girl with the extensive assassin and black ops training, while New X-Men expanded upon this further by revealing her to be a gifted strategist as well. Most writers now completely ignore everything after "highly-skilled fighter," and give her all the subtlety in combat of Leeroy Jenkins. This is most egregious in Avengers Arena, where the writers give lip service to her training and Awesomeness by Analysis, and still have her decide the best strategy for taking down Apex (who is controlling a Sentinel) is a direct frontal assault. Even the trigger scent has been subject to this. Initially, the conditioning the Facility subjected Laura to resulted in her rages focusing specifically on whatever was marked by the scent. By the time her solo series and Avengers Arena rolled around, the scent was now sending her after everything in sight.
Cyclops has suffered this himself over the years. He was always a little aloof and had some trouble socializing with those around him, he even had trouble telling Jean Grey, the woman he loved, how he felt even after they hooked up, and he was always under a ton of pressure that some times caused him to chew people out, but he has always had the best intentions for those around him and just wanted to keep his friends and loved ones safe as they fought for a better world. And then some very, very, very bad stories happened to him and as time went by more and more writers - and fans - came to see him as just being "that insanely repressed jerk who isn't Wolverine." Some writers do remember to give him positive traits from time to time though.
One of the chief gains of All-New X-Men, which brings the original team of X-Men into the future to stay with time travel, is that Teen Cyclops is a version of the character with both flaws and things working for him instead of a few redeeming qualities that very occasionally shine through an irrationally militant mindset, and who hasn't alienated most of the X-Men to some degree by being a total hardass.
Considering how often Cyclops and Havok end up fighting one another, they sometimes get Flanderized into being locked in an eternal Cain and Abel, being unable to abide one another at the best of times and one of them being a super-villain (usually Havok) at worst. This portrayal appears in the Ultimate, Legends, and Misfits universes, where (unlike their 616 counterparts) they don't need the influence of any psychic brainwashing to bait them into fighting.
A number of writers sadly only ever saw Jean Grey as either the Phoenix or "that cute girl Cyclops and Wolverine fight over." Jean Grey's reputation as the person who resurrects frequently has been further exaggerated, with Phoenix – Endsong demonstrating multiple deaths and resurrections over a few pages, further lampshaded in Deadly Genesis, when Scott and Logan react to the possibility of her resurrection in the same panel. In X-Men vol 4, the possibility of Jean Grey resurrecting was further discussed when her DNA became a plot point in the creation of a host for Madelyne Pryor.
Rogue’s sexualisation as a Ms. Fanservice is certainly this in the long run. Open up her first appearance in Avengers Annual #10 and it’s clear neither Chris Claremont or Michael Gordonth artist intended Rogue to be a icon of Perverse Sexual Lust to the Marvel masses, with her unsettling Cruella De Vi looking appearance. Even her now signature action of giving characters (usually guys) a Forceful Kiss was initially creepy and gross. Upon joining having a Heel Realization and joining the X-Men Rogue all suddenly started becoming more and more attractive and curvaceous with even the aspect of her character that she has to cover as much skin up as possible being often conveniently ignored as Rogue roller skated in a bikini or went around in Daisy dukes. Not to mention the Sensual Spandex of her outfit being played up to the hilt. Nowadays it’s more alarming when Rogue is played off as unattractive and sinister as seen by a Nightmare Sequence Carol has of her bridge fight with Rogue with the latter having a face of full of spikey teeth and glowing eyes.
Mister Sinister is an interesting case. Originally introduced by Chris Claremont as something of an evil cipher, little was known about Sinister other than that he was a Mad Scientist and that he was obsessed with Cyclops for some reason. Claremont had originally planned for a long, drawn-out reveal (in his usual style) that would have established Sinister as an 8-year-old boy with the mutant power of aging very, very slowly — as in, he was already over 100 years old when he was in the orphanage with Scott despite his body still being 8 — using the Sinister persona as a front. Claremont's abrupt departure shelved this plan, and so a new origin story was created for Sinister, one in which he was a scientist from Victorian England granted power and immortality by perennial X-Men Big BadApocalypse. This new origin story portrayed him as something of a Tragic Villain, and most of the stories of the time followed suit to greater or lesser degrees. But beginning with 2002's Weapon X a new interpretation for Sinister was introduced, one which hewed closer to the Claremontian Mad Scientist but also cranked his evil quotient up to eleven by making him an Expy of infamous Nazi scientist Josef Mengele. Since that time Sinister's become increasingly more affiliated with the Nazi regime, increasingly more Nazi-like in general, and increasingly more prone to playing the Politically Incorrect Villain.
Jimmy Hudson started in Ultimate X Men as the son of Wolverine, he had Wolverine Claws and a healing factor, but other than that he had his own personality, in many aspects in contrast with that of Wolverine. The comic played with this, balancing between the similarities and the divergences. The Ultimate Marvel comics ceased to be published in 2015, but he was rescued and incorporated into X-Men: Blue. In this comic, however, he became a full-time Wolverine Wannabe, a teenager "Wolverine" alongside the teenager's original time-displaced X-Men.
Professor X has often suffered from this with almost all post-Claremont writers. In Claremont's long stint, Charles Xavier was a kind-hearted mentor who was a little bit too stern and aloof at times. Subsequent writers would double down on the "stern" and "aloof" bits, to the point of Xavier being extremely manipulative, often lying to his students and with tons of shady secrets in his past. However, this is also a Revisiting the Roots of sorts, because the pre-Claremont Professor X that tutored the original X-Men was more often manipulative, secretive, and distant.
in). Originally her leotard covered her butt and if anything it was tamer than her first outfit which displayed her navel. Eventually artists got hornier and Carol’s well formed cheeks were larger and on nigh-constant display to point of In-Universe worship