Avengers: Back to Basics: The central problem in the last issue is that Kamala's mother Muneeba is hit by a bus and killed before her daughter was ever conceived, giving the latter only a few years to live before the timeline reaches the point where she should have been born and she puffs out of existence. However, issue #9 of Ms. Marvel (2014)'s second run, which was published earlier, established that Muneeba was already pregnant with Kamala when she moved to the United States. The issue isn't entirely insurmountable, as it's still entirely possible for Muneeba to have been carrying her unborn daughter when she died, but a number of the story's statements are made explicitly incorrected by this.
X-Men: The whole deal with the comics. A lot of it is the Kudzu Plot started with Claremont, but a lot of it comes from the loads of Ret Cons and counter Ret Cons.
One example is Jean Grey. Until the late 1990s, it was (relatively) simple. Jean was Jean. Phoenix was (retconned into) a cosmic entity that took her identity, and Madelyne Pryor was her clone. Then those Running the Asylum couldn't get that straight, and turned it into this. The Summers' Tangled Family Tree got worse and worse from the 1990s onward.
During Grant Morrison's run on the book, the X-Men travelled to China where a mutant named Xorn was held prisoner, released Xorn, and took him in as member of the team. Xorn turned out to be Magneto in disguise. The degree to which this made sense is debatable (since when does Magneto speak perfect Chinese? Why didn't Wolverine recognize his scent?) but it was at least easy to follow so far. But then Magneto started doing drugs and herding people into ovens, and when Morrison left the book, the remaining X-Book writers couldn't retcon him as an impostor fast enough. So it was someone pretending to be Magneto pretending to be Xorn. Then it turned out there was another Xorn, who was the brother of the fake Xorn. There's a reason they don't mention Xorn much these days.
How bad has it gotten? When Xorn reappeared on a team of Future X-Men traveling back in time for the Battle of the Atom, readers immediately assumed there was a surprise identity to be revealed. And they were absolutely right; this version was mind-controlled grown-up Teen Jean from the O5 team.
Somewhat amusingly, this trope is actually the reason Claremont was kicked off his second run on the title, as EIC Joe Quesada felt that his utter devotion to every minute detail of continuity made his stories nigh-incomprehensible.
An example of a Continuity Snarl only half caused by Claremont is that of Nova Roma and its inhabitants. As originally conceived by Claremont in the pages of New Mutants, Nova Roma was a Lost World city hidden deep in the Amazon jungle and founded by the immortal Vain Sorceress Selene during the days of Ancient Rome. One of its inhabitants, Magma, was established as being of blood relation to Selene (called her granddaughter, though more likely her descendant). But then years after Claremont left the title, new writer Fabian Nicieza came along with Retcons that Nova Roma was not actually ancient at all but merely a sham city full of people Selene had brainwashed, and Magma was in fact a British mutant named Allison Crestmere with no blood relationship to Selene. The two camps went back and forth on this after Claremont came back, until the continuity was so utterly wrecked that modern stories featuring Selene or the New Mutants tend to ignore both Nova Roma and poor Magma entirely.
During Marvel's "Acts of Vengeance" event, Wolverine fought Tiger Shark during his book's current story arc at the time. A few issues after that it showed while the other X-Men were doing at the time, and showed it was during the team's days in Australia. However, in their own book the X-Men team in Austrailia sans Wolverine had disbanded, had their memories wiped, and been scattered across the globe living under new identities long before the "Acts of Vengeance" crossover. It wouldn't be so bad if it wasn't for the fact that the X-Men's tie-in issues for the crossover were a key development for Psylocke, as it was during this event where she had had her mind transferred to the body of a Japanese assassin, a body she would stay in for nearly three decades before finally being restored to her original form. So in X-Men after the crossover she had her new body, while in Wolverine's book she still had her original body after the crossover. Whoops.
During the events of X-Men: Messiah Complex, it was said that Hope Summers would at some point end up killing millions, resulting in the Bad Future Bishop came from—which goes against what was already established about Bishop's future, which was Professor X (by way ofOnslaughtafter mindwipingMagneto) losing his mind, killing most of the X-Mennote A Red Herring was a survivor called the Witness, who was implied to be an older Gambit, and attacking the world being the cause.
A particularly funny one, elaborated here: In Uncanny X-Men #165, Kitty Pryde turns 14. In Excalibur #15, she turns 15. Both were by Chris Claremont, so we can assume this means that the events in between more or less follow Webcomic Time. The problem is, the period between 1983 and 1990 was a very busy period for Marvel, meaning that if you take the stated dates at face value, you end up with a rather bizarre timeline.
The Retcon that Wolverine's claws are part of his mutation and not implants tends not to mesh well with stories prior to the retcon. One story had the X-Men fighting the Morlocks, with the Morlocks employing Leech to cancel out everyone's powers to allow them to win through sheer numbers. However, Logan pops his claws, which he explicitly says are not part of his mutation, and that is apparent — because if they were, the claws would be gone at worse if Leech's powers took them away entirely, or he'd have hollow Adamantium knives in his arms he couldn't pop, since that's part of his mutation.
The Mighty Thor has been especially prone to this, originally because different writers simply drew on different myths. Soon enough however, after writers (like Roy Thomas) started contemplating the implications, Marvel Gods were gradually codified as beings literally formed from stories & empowered by belief. This has granted them and their lives a special metaphysical exemption from regular "mortal" time & space, resulting in the current line of thought; "he's a god, and contradictory stories about him can all be true, somehow". note This arguably makes most Thor lore immune to Continuity Snarl in the traditional sense, depending on one's interest in mythopoeia. Examples:
An early "Tales from Asgard" story shows Thor commissioning the creation of Mjolnir personally. Later stories have Odin using Mjolnir well before Thor was ever born.
Odin's wife was named Fricka or Frigga in early stories, until fairly recently when they decided she was Freyja. Yes, Frigga and Freyja are two distinct mythological figures, but scholars argue they may not always have been, so this wouldn't be too bad... except Freyja had already been established as separate from Frigga in the comics hundreds of issues prior note Plus, the Enchantress had previously been hinted to be Marvel's version of Freyja. Oy. . Not helping matters is that our new "Freyja" looked and acted rather differently from the Frigga we knew, yet the writers insist she's the same character.
Jason Aaron's run arguably has this regarding Loki. On the one hand, Loki is presented as a Momma's Boy, working as Frigga's secret double agent to undermine Malaketh's reign and wanting to make her proud. Except, over the course of Journey into Mystery (Gillen) and Loki: Agent of Asgard, its repeatedly shown that Frigga was terrible to Loki, blackmailing his innocent child into servitude and betraying his teen self to trap him into his villainous destiny. Which culminated in Loki, reincarnated as the God of Stories, making it clear that he does not give a damn about what she thinks of him. Furthermore, come Aaron's run (wherein Loki almost never mentions their new title), Loki acts more or less like a mix between his old (technically-dead) evil self and his MCU counterpart, rather than the Brilliant, but LazyDeadpan Snarker with good intentions he'd been recently, or the Chaotic Neutral Cloud Cuckoo LanderMeta Guy Brit punk the God of Stories was presented as. Then again, the entire point of Loki becoming the God of Stories was to embrace the mercurial, ever-malleable nature of Marvel godhood and never be beholden to one role again. So whilst Jason Aaron's distinctive styledefinitely doesn't suit the subtleties of magic and earns him due derision, his trivia-liteunpredictable hodgepodge approach to Loki made more sense than just treating "God of Stories" as a new list of traits and quirks to box him into all over again.note Seriously people go read Agent of Asgard, it's the most explicit thesis on this ENTIRE Thor section that's ever been published
A minor but still glaring example comes from the Heroes Return era run by Dan Jurgens and John Romita Jr. This series begins with Thor once more forced to take on mortal flesh by merging with and saving the life of a paramedic named Jake Olsen, who was critically injured during a battle between Thor and the Destroyer. Jake's partner, Demetrius, is seen stealing drugs from the hospital where they work and selling them and his internal narration shows him reacting angrily to the news that Jake is still alive, because he had planned to frame Jake for his own illegal activities. Thor (and Jake) subsequently leave Earth to search for the missing Asgardians, interspersed with scenes on Earth in which the police discover evidence implicating Jake as a thief and drug dealer; one would assume that Demetrius has made his move and framed Jake. When Thor returns several issues later, the cops show up and place Jake under arrest... at which point Demetrius emerges, reveals that he is an undercover detective and states that he has been embedded in the hospital investigating drug thefts for months. The evidence wasn't planted and Jake really was a criminal. This leads to him going on the run and the entire thing turns out to be an elaborate plot orchestrated by Loki to trick Odin into placing Thor's spirit in the body of an unworthy mortal, with matters complicated further when Jurgens introduces the idea that Jake had (or was) an evil twin called Loren. The issue is resolved and in the next story arc, Demetrius helps Jake to start putting his life back together. Throughout all of this, Jurgens seemed to forget that he had explicitly shown Demetrius to be the real crook back at the start of his run!
"We cannot change history. But gods do not have history. They have story. And that is something a writer always has the prerogative to twist." - Loki
Is Marvel's Superman equivalentThe Sentry a Silver Age hero who erased all knowledge of his existence so an evil being called The Void would not exist? Or is he a superhuman with mental problems who read a comic book and adopted the identity? Is he the results of Super Serum experiments with The Void being actually a part of his fragmented mind? Who knows?
No, wait, he's a drug addict who accidentally drank God to get high. No, wait, he's the Angel of Death. No, wait, he's dead now. By the time they'd reached this point, the universal fan reaction basically boiled down to "good riddance".
When Paul Jenkins wrote the original Sentry miniseries, he was very aware of all the problems involved in introducing a schizophrenic Reality Warper with a Superman obsession and a mid-life crisis into the Marvel Universe. The series actually explored this theme at some length - and ended in a way that should have pushed the Sentry offstage forever. But a guy that broken just couldn't resist thinking up new excuses to keep the fantasy going.note Not anymore than the Bullpen could resist bringing him back about three times too many.
One of the original reasons for creating the Ultimate Marvel universe was to avert this trope by creating a blank slate free from the decades of continuity the main universe had built up. This didn't stop Ultimate Marvel from generating Continuity Snarls of its own.
One snarl concerns its version of Iron Man. The Ultimate Iron Man miniseries by Orson Scott Card, while good on its own, depicted Tony Stark as superhuman born with a healing factor and his brain distributed throughout his entire body. Since the Ultimates series depicted Tony as the more traditional nonpowered genius in power armor, this caused issues. Another origin story featured in an issue of Ultimate Marvel Team-Up created further problems. Although Brian Michael Bendis, who wrote the latter story, has suggested that some of Ultimate Team-Up is dubiously canon, it remains to be seen how or if the former will be reconciled.
The Ultimate Iron Man miniseries was later retconned to be an anime about Tony Stark's life that ignores the truth in favour of bizarre sci-fi, though that didn't stop the 'distributed brain' thing from showing up elsewhere.
In Ultimate Spider-Man and The Ultimates the Fantastic Four are referenced and Reed Richards is a notable enough scientist to have a building at ESU named after him, but very early on in Ultimate Fantastic Four, before the team comes together, there are references to The Ultimates. This is because of a change in plans. Originally, the Fantastic Four we were seeing in Ultimate Spider-Man and The Ultimates were going to be adults, while Ultimate Fantastic Four would take place a decade or so in the rest of the line's past, establishing the FF as the first super heroes and cornerstones of heroic society in the Ultimate Universe. The plan got muddled and changed, but it's very apparent when Sue Storm, 16-ish here, shows up during Ultimate Spider-Man's "The Clone Saga" and is clearly in her late 20s/early 30s.
Ultimate FF: While revealing that the Doom who kicked off the events Ultimate Power, The Ultimates 3 and Ultimatum and died was really Mary Storm, a new one was created: namely Doom calling out for Storm in the last of those events after Magneto's actions resulted in Latveria being frozen and is additionally compounded by Mary attending her ex-husband Franklin's funeral, which takes place after the Thing killed the Doom who caused those events.
Bendis initially established that Spider-Man's parents died in a plane crash, only to later reveal that they died at the Hulk's hands. He would eventually admit that he had forgotten he had already given them a backstory. This would be retconned so that they were only injured in the Hulk's rampage.
A bad example comes from the Ultimatum tie-in arc in Ultimate Spider-Man. Issue 131 sees Peter and the Hulk discover Daredevil's body and Peter remark that he didn't know who Daredevil was until Bruce said something — which ignores that he learned it in the "Knights" arc as Peter was personally recruited by Matt in their respective civilian guises, with Matt introducing himself by name and stating he was an attorney and Peter was even there when Matt's law office blew up.
The original Ultimate Daredevil & Elektra subjected the latter's father to Adaptation Name Change, going from being named "Hugo" to "Stravos" with his background having been that he was born in the United States — then the Sequel SeriesUltimate Elektra, his name was changed yet again to "Dimitris" and his background was now he was an immigrant.
The Destroyer is a Golden Age Timely Comics character who got his powers from a Super Serum. That's about all anyone can agree on about him. For instance, is he named Keen Marlow or Brian Falsworth? If he is Keen Marlow, how do you spell it? Keen Marlow, Keene Marlow, or Keene Marlowe? Or is Keen/e a nickname, and his real name is Kevin Marlow? If he's Brian Falsworth, where did the name Keen Marlow come from? Was it a pseudonym he used while working as a spy? Did he ever go by that name at all? Finally, did he begin his Nazi-punching career before or after Captain America, and if after, was the serum used to create him based on the one used to create Cap or not? *Whew!*
The Crossing, a Crisis Crossover featuring The Avengers, is such a snarl that even Linkara refuses to review it, partly because it's nearly impossible to tell when it begins or ends.note It has since been released in trade paperback form, a copy of which Linkara's holding front and center in his 2016 opening credits, so it's now under consideration for a future review. Basically, Iron Man turns evil and helps Kang try to take over the world, but who is on whose side changes from issue to issue. Eventually, Kurt Busiek rendered the whole thing moot in Avengers Forever by stating that the entire thing was Immortus trolling the superhero community so that they'd leave other planets alone, and that almost everyone involved was a Space Phantom. After the Heroes Reborn/Heroes Return debacle, the Crossing was pretty much never brought up again.
Avengers Forever: Busiek uses the series to untangle the very snarled continuity of The Vision. For decades, the Vision's origin story had him being created from the remains of the original Human Torch. However, after the writers of West Coast Avengers decided to re-introduce the Torch to modern continuity in the late 80s, the Vision's origin was retconned, invalidating a lot of stories and raising a lot of questions about where the Vision did come from. Enter Busiek, who explained everything by having Immortus use a time-altering MacGuffin to change history, so that two contradictory events, the Torch being rebuilt and the Torch not being rebuilt, both happened at the same time. Neat, huh?
During Busiek's run, some years before, the Vision and the Scarlet Witch remembered their sons without either of them losing their sanity.
When closing the mansion, Stark mentions that he had stored and taken away all the fancy materials and technology. Still, when the Young Avengers fought against Kang in the abandoned mansion some months later, they had no problem finding several old weapons of the Avengers.
And the infamous one — Doctor Strange tells the Avengers that there's no such thing as "chaos magic," despite having used it himself in his own solo series. This was later explained by Chthon himself, who said that the Sorcerers Supreme and others had tried to limit his power by saying that there was no such thing as chaos magic.
The symbiotes. First, the Venom suit was just an alien costume. Then it was retconned into being alive. Then, when the writers wanted to turn it into a villain, it was retconned that the suit made Spider-Man go insane and he had to get rid of it (originally, he was trying to destroy it just because it was attaching itself to him, which is a bit harsh for a guy like Spidey). It was later shown that the suits fed off strong hosts as a sort of Social Darwinist. Then it was revealed to feed off negative emotions such as hate and anger. Then they were shown to live in the Negative Zone... no wait, there was a separate planet full of them. Oh, and Toxin proved that not all of them are born evil after all. Oh, and Carnage has had about three symbiotes get destroyed but no one ever remembers those stories. And now the Venom symbiote itself wasn't evil until it latched onto Deadpool, who tried it before Spider-Man came by and ended up absorbing Deadpool's insanity (at least if you consider Deadpool's Secret Secret Wars canon).
Who is the Hobgoblin really? The character was created by writer Roger Stern who strung along the mystery of his identity, dropping clues here and there. According to him, when he created the Hobgoblin he didn't have a set idea of who he was, and only shortly into it did he decide it was a character he had introduced in a smaller title called Roderick Kingsley. Then he left and told his plans to his successor Tom Defalco who didn't like the culprit and Stern told him that he had his consent to come up with someone else. Later writers and editors felt that the Hobgoblin mystery was itself compelling and so spun wheels and Red Herring to extend the story forward, until they and readers got bored and frustrated, and finally it was revealed that Hobgoblin was Peter Parker's friend Ned Leeds, who had already been Killed Off for Real when this reveal happened. It is no wonder years later Roger Stern was allowed to return to the subject in a miniseries which was essentially a Fix Fic in which Stern gave the identity to the person he'd intended all along, and established that Leeds had been brainwashed into acting as a stand-in who was later sacrificed so that the original could retire. It helped that Stern had, in fact, established Hobgoblin's use of impostors during his original run.
Post-One More Day, Harry Osborn somehow still being alive all this time but Out of Focus is something that Marvel writers never fully explained since doing so would have to get them to explain what happened in Revenge of the Green Goblin a story arc where Norman tries to torture and gaslight Peter into becoming the Goblin after his revival, an action that was inspired by Harry's death during his exile to Europe and simply doesn't make sense in tone and motivation with Harry somehow still being alive through it all. Writers have simply not alluded to this elephant in the room and merely bypassed it.
Part of Mephisto's deal had Peter's identity becoming secret again, but OMD and the follow-up One Moment in Time (which is essentially a reboot and retelling of OMD) created a Continuity Snarl where according to the story, Doctor Strange who erased everyone's memories of Peter Parker being Spider-Man did so for those who didn't know the identity before Civil War, but this doesn't explain how Norman Osborn and Black Cat forgot his identity despite knowing his identity well before that.
Spider-Man: Blue: The mini-series has several continuity errors that can be picked up on by avid readers. These include;
Robbie Robertson working at the Daily Bugle, despite not being introduced at that point in the original comics.
The circumstances of the Green Goblin losing his memory are different.
In this comic, Peter comes from a fight with the Rhino to meet Mary Jane Watson and take her to a fight with the Lizard. In the original comic, it was the Rhino he took MJ to meet.
The fight with Blackie Drago, the second Vulture, is completely different from its original incarnation, taking place in the wrong time and under the wrong circumstances.
Furthermore, Drago's fight with the original Vulture was supposed to be over before Spider-Man got there.
The original story featured a subplot with Peter spraining his arm, passing out from the pain, and getting captured by the police, which is entirely cut.
It was originally Kraven's intention to attack Harry Osborn; he was not confused in his search for Spider-Man by Harry wearing Peter's aftershave.
However, these could be theoretically explained by the series' format of Peter narrating the story on audiotape to himself. Perhaps his emotions got his head a little clouded.
Starbrand & Nightmask made the aforementioned Kenny McFarlane, a character created for Ultimate Spider-Man, into a Canon Immigrant, it adapted him as a college student and in the same age range as a young college student. Issue 35 of Venom (Donny Cates) introduced a character named "Kenny McFarlane Jr.", so unless his dad is a separate person who, much like the Ultimate version, did go to school with Peter and Flash, it's unlikely that the Kenny of Starbrand & Nightmask could father a high school-aged student.
As a consequence of dropping in the middle of several large, running storylines, Marvel's Avengers NOW! relaunch has resulted in some major continuity issues. The biggest one involves the plot point about Steve Rogers experiencing rapid aging and passing the Captain America mantle to Sam Wilson. This particular plot thread happened to come about at the same time Jonathan Hickman was prepping his big Time Runs Out crossover between The Avengers and New Avengers, the main crux of which involves the war between Steve's team (the Avengers) and Iron Man's team (The Illuminati). Despite the fact that "Time Runs Out" explicitly shows a still-young Steve vowing to hunt down Iron Man and his teammates (meaning the conflict definitely began before Steve was aged), other stories like AXIS show the elderly Steve still working side by side with Iron Man without any animosity between the two (even before Tony was turned evil, by the way).
Brian Michael Bendis's work had tended to have some of these — but a pretty big example is the aforementioned Avengers Disassembled. Another is the first arc of the Avengers Assemble comic also has some issues: Iron Man also says "We barely know anything about Thanos" — despite the Avengers fighting him on numerous occasions (including partaking in the fight in The Infinity Gauntlet and its sequels) and having extensive files on him, and Thanos debuting in an Iron Man comic and thus Tony Stark himself was the very first Avenger to do so. Another thing was stating Thanos' goal was "He wants the Earth. He's always wanted the Earth," when in nearly every single prior encounter Thanos has ignored the Earth entirely.
This can be a problem when a character who was seemingly killed off is later revealed to have actually survived:
After The Wasp's death in Secret Invasion (2008), Hercules ran into her in the Greek afterlife, where she was shown alongside a number of other dead Marvel characters. However, it was later established that she'd never actually been dead, and that the explosion that seemingly killed her had actually just trapped her in the Microverse.
In the X-Statix Presents: Dead Girl mini-series, Mockingbird appeared as a supporting character in the afterlife. The above-mentioned Secret Invasion later established that the Mockingbird who had died all those years ago was actually just a Skrull impostor who had replaced the real Mockingbird after she'd been kidnapped.
During J. Michael Straczynski's Thor run, he had Thor meet the departed spirit of Captain America, who had recently died at the end of Civil War. The later Captain America Reborn mini-series established that the gun Cap had been shot with was actually a special device that merely sent him through time rather than killing him.
In an issue of The Sensational She-Hulk, she has a near-death experience where she gets to spend some time in the afterlife (ultimately meeting with her mother), during which she meets up with Bucky in the afterlife mall. This was about a dozen years before the Winter Soldier story established Bucky was never actually dead, but being kept in intermittent cryosleep by the Soviet government. Norman Osborn was also there, a few years before he resurfaced in The Clone Saga.
The Spider-Woman named Jessica Drew has at least three different origins:
Originally, she was one of the High Evolutionary's experiments in engineering new humanoid species from animal stock; in Jessica's case, she was a spider artificially evolved into a perfectly humanoid form.
Then she became the daughter of a pair of scientists who was poisoned by the uranium deposits near their lab; her father injected her with a serum made from spider genes in an effort to cure by infusing her with the resistant to radiation possessed by spiders. He then put her in a "genetic accelerator" to enhance the serum's progression, which caused her to A: gain spider-powers, and B: rapidly age until she was a child in the body of a young adult. The "spider evolved into a human" backstory was retconned as a false set of memories implanted in her.
Another comic, "Spider Woman: Origin", retcons it again, most notably stating that whilst her parents were experimenting on a way to graft useful genes from spiders to humans, Jessica's pregnant mother was zapped with a splicing beam and Jessica was imbued with spider-genes in her mother's womb.
The concept of Deadpool Kills the Marvel Universe was revisited with an alternate continuity series named Deadpool Kills the Marvel Universe Again with evidence at the end to suggest that it's really a Stealth Prequel to Old Man Logan — except, even putting aside the Ambiguous Ending of whether or not Deadpool killed the Red Skull and his allies or if his mind is too far gone and he's delusional, there's things that contradict the original Old Man Logan, like Jane Foster as Thor.
It's really not an exaggeration to say that Kang the Conqueror is more or less the Anthropomorphic Personification of this trope. The character's concept is simple enough, but unfortunately lends itself to becoming an insane continuity headache the longer the franchise progresses. Kang is a mighty supervillain and, well, conqueror who built a grand empire in the far future and employs Time Travel to further his schemes, ensure his own existence, and improve his situation. The idea, presumably, was that Kang is a Non-Linear Character; we see Kang in different identities (Kang, Rama-Tut, Immortus, Scarlet Centurion, Iron Lad, etc.) and at various points in his timeline, always engaging in myriad schemes in Anachronic Order and then one day it would all be shown from his perspective and make sense. Unfortunately, with the simple realities of comic book storytelling (such as the large number of different writers), this ambitious idea quickly collapsed under it's own weight and Kang's timeline became an insane tangled, gnarled mass of paradoxes, colliding plots (both the in-story kindand the out-of-universe kind), timeline splits, alternate selves, and general timey-wimey nonsense. Now, after so many years and twists and offered explanations, it's become genuinely hard to tell who or what Kang is even supposed to be or is trying to accomplish at any given point in time beyond the basics of "is engaging in Time Travel for Fun and Profit", and even Kang himself seems to struggle to keep it all straight in his head. Kurt Busiek made a noble and temporarily-successful effort to untangle the whole mess with Avengers Forever, but that was decades ago now and Kang's history has grown since. It's all made infinitely worse by the fact time travel itself functionally doesn't actually exist in the Marvel Universe, the long-established lore being that anytime you "time travel", you really just jump to a Close-Enough Timeline that splits off from your own (e.g., in Days of Future Past a Kitty Pryde from a Bad Future goes "back in time" to prevent said Bad Future and succeeds, but when she returns home nothing has changed; she prevented the Bad Future for the 616 timeline not her own). This extra complication, naturally, just serves to make Kang's story even more kind-numbingly complex.
Ghost Rider might be the most genuine unironic example in Marvel's entire mythos! They retconned and re-retconned and re-re-retconned what the hell Ghost Riders are and where they came from and what their purpose is so many times that the Ghost Rider comics themselves started pointing it out and making fun.
Quicksilver and the Scarlet Witch's parentage:
The first time it was even established this was a question was in Giant-Sized The Avengers #1, in which Golden Age hero Bob Frank/the Whizzer was almost certain they were his, since his wife Madeline Joyce/Miss America had died in childbirth on Wundagore Mountain and he had fled in grief, but not before seeing they were opposite-sex twins. For the next few years they actually used the surname Frank.
Five years later in Avengers #182, the twins would meet Django Maximoff, who insisted that they were his long-lost children Ana and Mateo Maximoff. This lead into "The Yesterday Quest!", which eventually revealed that they were the children of Magneto and his wife Madga, who after leaving him had also given birth on Wundagore Mountain. The previous story was explained as Miss America's child being stillborn, but Bova had passed them off to the Whizzer both to assauge his grief and because Magda didn't want Magneto to find them (and he didn't, the fact they later joined the Brotherhood of Evil Mutants was a complete coincidence). Django and his wife Marya had recently lost twins (the actual Ana and Mateo), so when Whizzer fled, Bova instead asked them to raise the twins. That was the status quo for decades.
Then Marvel decided to decouple the Maximoffs from X-lore to tie in with the Marvel Cinematic Universe versions. So AXIS revealed they weren't actually mutants, and Uncanny Avengers: Counter-Evolutionary established that they were in fact the children of Django and Marya Maximoff, who had been kidnapped by the High Evolutionary and experimented upon, then returned. It wasn't really explained how Magda and Miss America fitted into this, or whether this meant they actually were Ana and Mateo or the Maximoffs had had two sets of twins.
And then, Scarlet Witch (2015) reveals they were actually the children of Django's sister Natayla Maximoff, who was the previous holder of the hereditary title of Scarlet Witch and had entrusted them to her brother and his wife, before dying trying to rescue them from the High Evolutionary.
But despite all this, X-Men: The Krakoan Age kind of wants to pretend Wanda's still Magneto's daughter, even though it has to pay lip-service to the status quo being that she's not.
The events of Uncanny X-Men, Vol 1. #335, which saw Moira MacTaggert and Excalibur aware of what was going on and that some of the X-Men are on their way to Muir Island, and Wolverine set off on his own to get answers about the origin of Onslaught, are contradicted twice:
Excalibur #100 saw the titular team busy still dealing with the Hellfire Club's London division — making this one a double-edged sword said Uncanny issue itself ignored that this was a story already underway — and Moira was surprised by the X-Men's visit.
Wolverine, Vol. 2. #104 sees Wolverine claim that Cyclops and Jean told him to meet with Gateway to get answers about Onslaught's origin. Even ignoring that in the Uncanny issue, they didn't and the decision for Logan to go off was his own, the Uncanny issue sees the mission be pointless as it also has the Avengers and remaining X-Men suss it out on their own: It started with Xavier mindwiping Magneto following the latter ripping out the adamantium from Wolverine.
Thor sports his shirtless "World Engine" look for most of it, switching out to the infamous Mike Deodato-created croptop look in the last issue of his own — and then switched back to the shirtless look in Onslaught: Marvel Universe. Then again, he was switching between the two looks before that point (including sporting the croptop one in Marvel Versus DC) before this point. Likewise, the Falcon was sporting an armored look at the time, but in Onslaught: Marvel Universe, he was back in his classic 1970s costume.
The last few months of The Clone Saga included Red Skies Crossovers with Onslaught with Sensational Spider-Man, Vol. 1 #8 seeingm then-current Spider-Man Ben Reilly get involved with dealing with Sentinels, which ran through Amazing Spider-Man, Vol 1. 415 and Spider-Man, Vol 1. #72), whereas Spectacular Spider-Man, Vol 1. #238 saw Ben chasing the Lizard creature while the invasions of Sentinels going down. For that matter, the end of Spider-Man #72 saw Ben and Peter resolve to be part of the final battle against Onslaught, but are absent in Onslaught: Marvel Universe.
Magneto started doing drugs and herding people into ovens, and when Morrison left the book, the remaining X-Book writers couldn't retcon him as an impostor fast enough. So it was someone pretending to be Magneto pretending to be Xorn. Then it turned out there was another Xorn, who was the brother of the fake Xorn. There's a reason they don't mention Xorn much these days.
: In Uncanny X-Men #165, Kitty Pryde turns 14. In Excalibur #15, she turns 15. Both were by Chris Claremont, so we can assume this means that the events in between more or less follow Webcomic Time. The problem is, the period between 1983 and 1990 was a very busy period for Marvel, meaning that if you take the stated dates at face value, you end up with a rather bizarre timeline.