The Avengers: During Geoff Johns' run, the Red Skull infiltrates the U.S. government and manages to unleash a biological weapon that spreads across several states, killing thousands. The consequences of this horrific and unequalled terror attack? Nothing. No-one ever mentions it again.
Captain America has often handed his shield and title to other people. John Walker, Bucky Barnes, and Sam Wilson, respectively because Steve had become disheartened with the role, was thought to be dead, or had been Brought Down to Normal. Each of those has eventually end(ed) with them stepping down and handing the title back in order to return to their own personal identity. Almost subverted with Bucky, though, as Steve had believed that being Captain America was a good thing for Bucky, and when he returned, he opted to take a promotion to becoming the new top-dog of S.H.I.E.L.D., making him something of a general to the superhero populace, rather than the field leader of the Avengers. This, largely, was thanks to fan reaction towards Bucky!Cap being so overwhelmingly positive that many fans didn't want Steve to come back to the role. In the end, he only returned to the role as it was in order to coincide with the Marvel Cinematic Universe.
Sam Wilson became the official Captain America in Captain America: Sam Wilson. In Captain America: Steve Rogers, Steve Rogers returned to normal and subsequently shared the identity with Sam for a while, with both men using the Captain America name. This lasted until Secret Empire and Generations, which ended with Sam giving the shield back to Steve and returning to his original Falcon identity.
The Fantastic Four are one of the few comic teams where the members change uniforms and actually stick with the new duds. (Except one case where Sue once tried a Stripperiffic outfit that exposed her cleavage and midriff; it just wasn't her, and surprisingly, the fans knew it. She got rid of it quickly.)
Poor Benjamin Grimm will always be The Thing. Reed Richards' various attempts to find a cure to his condition will never work, or if so always be reversed. This is lampshaded in Marvel 1602 where Reed Richards, theorizing that stories are laws of the universe, states that a cure for Benjamin wouldn't last long since he's much more interesting the way he is.
Averted in the Ultimate Marvel universe, following the end of Ultimate Fantastic Four. Ben Grimm does in fact manage to shake his rock-like form, and gain all-new powers which include the ability to switch between his regular human form and his rock form.
In Fantastic Four #403-405, the team visits an Aztec temple discovered by archaeologist Ken Robeson. The abandoned temple can harness cosmic rays which may have killed off the original tribe. The Thing visits the temple and is briefly turned into human form. The technology is never used for this purpose again, and by #416 it is said to have been dismantled to help fight Onslaught.
Not only can Doctor Doomnever be killed for real, but he'll never lose control over Latveria for too long, since him being King and Dictator is a very important part of the character's concept. Is there such a thing as Joker Diplomatic Immunity? Also, his face will never get better, though this seems to be a conscious decision on his part so that he'll always have a permanent reminder of Reed's "crimes" against him. While his face was finally healed at the end of Secret Wars (2015), this only lasted until the final issue of Brian Bendis' Invincible Iron Man run, which once again had Doom get disfigured during a fight with the Hood.
The Incredible Hulk: Poor Bruce Banner will always be the Hulk. He will never find a permanent cure, and because of that, he and Betty Ross will most likely always be Star-Crossed Lovers. Things might have changed with Betty Ross becoming the Red She-Hulk, but she permanently lost her powers.
This was predicted by Kieron Gillen concerning Loki; he would eventually go back to his usual self after Gillen had him reverted to childhood with about half his memories, practically worshiping The Mighty Thor. Much of the impact of the arc was not from wondering if the change would stick, but on the possible effects once things reverted to Status Quo. As writer of the Thor title (renamed Journey into Mystery (Gillen) thanks to the focus on Loki, rather than Thor), he indicated that Loki turning evil again WAS NOT a foregone conclusion, as Thor destroyed the Ragnarok cycle which contained the writings that decreed the destinies of the Asgardians, enabling all of them to Screw Destiny, Loki included, but in the end, Loki's villainous side returned. The writer says he chose to end the story with Loki's return to evil because he knew that if he didn't, someone else would come along and do it anyway. And at least if Loki fell from grace under his pen, he could do it in a suitably emotional manner. "So-and-so IS NOT a foregone conclusion" has been said numerous times (see Joe Quesada talking about the Spider-Man identity reveal, saying "it won't just be undone by magic a year later". So take any promise of permanence with a gigantic grain of salt.
HOWEVER, this was ultimately subverted in the end. Loki's adventures were continued in Gillen's Young Avengers run, with them now developing a massive Guilt Complex over his villainous' side returning, ultimately revealing that Loki's dark side hadn't returned; rather, their mind and memories had been restored but they retained the morality of their young self, and after they were restored to an older form (if albeit still younger than traditional, being now a 20s-something), they're now having a solid go at a Heel–Face Turn in Loki: Agent of Asgard, with a big focus on how they're attempting to Screw Destiny, with their future self, who had inevitably returned to villainy, playing the role of the Big Bad.
Zig-zagged in The Immortal Thor. Loki is once again an antagonist, but is Ambiguously Evil, and Thor believes that his brother must have a reason to resume the role.
Morbiusthe Living Vampire will always be a living vampire. Despite being cured of his pseudo-vampirism several times over the years, sooner or later he's always reverted back. He was once killed and brought back as an undead being, but, true to his name, ended up going back to 'living' about a year later. He's also worn several costumes over the years, including a leather outfit in his first solo series, but eventually always goes back to his signature outfit, the one he was introduced in.
Speaking of Spider-Man… As of the Spider-Island arc, his current girlfriend dumped him, the psychic block preventing people from learning his secret identity is gone, and he and MJ have decided to rekindle their relationship. It also gave Spider-Girl back her powers, which she had lost a few years ago, and Eddie Brock is no longer Anti-Venom.
Spider-Man has also gained new abilities at several times over the years (such as poisonous stingers from his forearms and organic webbing like inthe movies). He once grew four extra arms in a failed attempt to remove his powers (he was probably glad that was temporary). He always loses these quickly enough and reverts to his original Stan Lee / Steve Ditko powerset.
Spider-Man seems to have gained two distinct Status Quos: He's either a single young adult living either alone, with his aunt, or a close friend, or he's married/in a committed relationship with Mary Jane Watson who he lives with, and appears to be growing up. This is the result of two parties Running the Asylum; in the former case, people who grew up with single young Spidey and/or cling onto him as a means to cling onto their own young adulthood, and so insist on keeping him this way, and in the latter case, people who grew up with Spidey when he was dating Mary Jane who, thanks to being the Ensemble Dark Horse, became a Fan-Preferred Couple with him, and so they make it canon and have them settle down since that's the logical path for a relationship to go, and likely similar to how the writer is currently. Because of this, Mary Jane has repeatedly been Put on a Bus, often via a means to try and ensure that she doesn't come back (such as killing her off or Derailing her), but every time this happens she always comes back (usually because whatever prompted her to leave, she gets over and reunites with Peter because ultimately, they both love each other too much). This is similar with any prominent relationship in mainstream comics; Superman and Lois Lane, Batman and Catwoman, Green Arrow and Black Canary, Aquaman and Mera, Ant-Man and The Wasp, Iron Man and Pepper Potts, Hawkeye and Mockingbird, and many, many others are pretty much stuck in an endless cycle of being broken up by writers who prefer them single and reunited by those who prefer them together. Because of this, fans of either persuasion should be able to rest easy, because sooner or later, they're going to be the way they want them. For a while. (In practice, of course, whichever set of fans is currently not being served call loudly for the Reset Button to be pushed now.)
Exactly where Venom sits on the moral compass is entirely based on whatever the writer wants to do with him, but while he usually lands somewhere in the Anti-Hero quadrant the symbiote has changed hands so often it's hard to keep track. Eddie Brock became Anti-Venom after abandoning the symbiote because its bloodlust grew too powerful for even him to control, going through a Faith–Heel Turn leading up to his new identity and seeing all symbiotes as diseases to be purged. But after giving up the identity, he wound up bonded to another symbiote, Toxin, whom Flash Thompson (who was the new Venom at the time) pointed out he had gotten rather buddy-buddy with. When the two parted ways, Eddie told Flash that when - not if - he lost control of Venom, Eddie would turn up to put him out of his misery. Jumping ahead a few years, Eddie spontaneously turned up after both had been separated from their respective symbiotes to retrieve his old one, referring to it as his "beloved" and promptly becoming Venom again. And that's not even getting into how the symbiote itself and its characterization has jumped all over the place, with a total purge of its dark side taking place in Guardians of the Galaxy to help introduce new readers who had never known Venom was ever a villain only to undo it under a villainous SucksessorLee Price a year or two later.
Dr. Octopus gets it almost as bad as Peter when it comes to this. Anytime he seemingly gets killed, undergoes Character Development, gains greater strength to fix his Glass Cannon issue, or does his best to pull a Heel–Face Turn, he'll always be brought back as the villainous Doc Ock to be Spider-Man's Arch-Enemy. It started when he suffered his first death at the hands of Kaine and was brought back to life later. Some years later, he suffered brain damage from all his years of battle with Spider-Man and managed to switch bodies with Peter, becoming the Superior Spider-Man and after a short run, relinquished the body back to Peter, seemingly dying as a hero who redeemed himself. Later on, he returns as a villain and even got a more powerful body, eventually saving May from Red Goblin and winning a second chance from Peter as a result. After that, Otto went back to being the Superior Spider-Man in San Francisco, becoming an effective, if brutal, hero but after a short run, experiences his own equivalent of One More Day where, to defeat an alternate version of Norman Osborn who had Octavius in a really bad spot, he had to make a deal with Mephisto to give up all his memories of being a hero and his empathy for others. As a result, Otto lost his friends and new love interest in the process, with the end result being that once more, circumstances of the story will always conspire to return him to being the villainous Dr. Octopus.
This was actually lampshaded in the final issue of U.S.Avengers as Sunspot, despite having bought out AIM and turned it into a force of good, noted there were always small pockets of the evil version ready to rise up and take their place.
Charles Xavier was introduced as an invalid who uses a wheelchair. Several times during the comic's run, Xavier has regained the use of his legs. It's only a matter of time until something reverses this situation, either undoing whatever allowed his legs to heal or sustaining a new injury.
Marvel seems to think the concept of the X-Men doesn't work if mutants aren't feared and hated by everybody even there are a good amount of series that shows it can work, So any progress they make is inevitably undone to the chagrin of readers. However this has started to change in the 21st Century.Grant Morrison's run had mutants gaining some acceptance among the younger generations and developing their own culture. Then House of M comes along and the mutant race is reduced to around 200 survivors. And then comes Avengers vs. X-Men, where thanks to the actions of Cyclops and the Phoenix Five, mutants are once again repopulated. In a strange twist though, mutants are more accepted now, especially by leftwing college students (similar to how LGBT rights tend to be a sticking point for this crowd in real life) after Cyclops' actions, both during the decimated time and as a Phoenix avatar where, in the former, he did a lot to gain good press for mutants as well as reminding people how powerful the X-Men are and unwise it is to attack them, and in the latter, used his godlike power to better humanity and solve many third-world problems. But, government handling has now intensified with the renewed risk of omnipowerful mutants wrecking havoc, Police Brutality has became more common, and mutants who can't defend themselves and live in hostile areas are in serious risk. In general, things have finally gotten better but still have a long way to go, which is a reality for real life minorities.
Speaking of X-Men, Rogue possesses the power to absorb the psyche and powers of those she touches. When she was first introduced, these powers were uncontrollable and this fact was often a source of angst for her. Her powers would frequently change and she would even occasionally lose them, only to have them inevitably return as uncontrollable as ever. Then, after nearly thirty years of publications, Rogue finally gained control over her powers during Messiah Complex with help from Professor Xavier. However, come 2014 and Uncanny Avengers, Rogue has once again lost control over her powers and has permanently absorbed Wonder Man's power and psyche, essentially reverting her to how she was when she was first introduced. She even goes on a crazed rant about how she'd been through the whole ordeal already and commented that she couldn't even stand the thought of having to do it again. Having Wonder Man in her head probably didn't help either.
Grant Morrison created the villain John Sublime as meta commentary on this trope. Mutants are a natural threat to him, so he intentionally manipulates events to keep them in a constant state of cyclical fighting so they can't band together and stop him.
Sabretooth is the newest case. He was inverted into a good guy during AXIS and decides to follow Logan's example by finding his own Wolverine. The first book he was in got cancelled due to Secret Wars (2015), then he went to Bunn's Uncanny X-Men. He joins the team & continues his quest for redemption while developing buddingrelationship with Monet St. Croix, whom he was very protective of. His inversion showed signs of slipping & he struggles to fight the reversion. Not wanting to be a monster again, he vows to become something different if he can not stay inverted. He also uses helping Monet as motivation, who was cursed by her brother and became a vampire. He eventually ran away with her at the end of the series. Cue Resurr Xion, and all of this has been ignored. His struggles with not wanting to be a monster haven't come up, and his entire relationship with Monet was dropped without any explanation. He's back to wanting to kill stuff in Weapon X, with Logan & Warpath keeping watch on him and being ready to kill him should he lose it, but trying to keep him sated by looking for monsters & villains he can fight. The Claws of A Killer mini also shows he's back wanting to kill Wolverine when he hears that he may be alive again. The end of Weapon X (2017) sees him driven insane in hell and returned to an almost-feral state, all semblance of positive character growth rendered completely null.
In Curse of the Mutants, Jubilee, recently depowered, was turned into a vampire and stayed like that for a while after. Can't have something as cool as inventive as a vampire x-man, can we?
The cyclical nature of comics was lampshaded in an issue of New Avengers, where Wonder Man points out that the entire Civil War crossover was utterly pointless since everything (more or less) went back to normal within just a few short years.
