Franklin Richards on the side of good. His powers are so great, he was able to create the Heroes Reborn universe. Unfortunately for the heroes but fortunately for any sense of drama in the stories, he's too young to understand how powerful he is - and usually when he is old enough, his powers degrade to 'merely' very strong Psychic Powers out of what is initially suggested to be a belief in limits, and more recently, what is implied to be a fear of either losing control or having to live up to his almighty future self.
Nathan Summers being the child of Scott Summers and Maddie Pryor, a clone of Jean Grey, in a complex scheme enacted by Mister Sinister in order to subvert his creator and master Apocalypse. Is stated by many to be such a powerful (or potentially powerful) psychic of the highest order that there's practically nothing his mind cannot accomplish, when he's unhindered by the T.O. virus. Or to put it another way, Cable is the mainstream reality counterpart of Nate Grey (see below), and as 'Saviour Cable', went toe to toe with the Silver Surfer while simultaneously repairing everything their fight was destroying and holding the vast island-city of Providence in the air. As he put it, while smashing the Surfer's board, "I didn't turn myself into everything I ever fought against, a god, just to come up short!"
Nate Grey, who was created by the more direct route of simply taking a bunch of Scott and Jean's DNA and mixing it together, spends some time hanging out and bonding with Franklin, is a psychic so powerful that he falls into this category. Instances include occasionally rewriting reality in his sleep and stopping time by accident. And that was before his powers were fixed. After a certain point, he evolves beyond the need to do things like eat, sleep or even breathe, and treats the multiverse as his personal stepladder, to be ambled up and down at will, having comfortably destroyed an evil alternate version of Jean Grey, reunited a woman who'd split herself across thousands of realities, easily went toe to toe with someone who was at least a planet buster, if not a reality buster, then transformed himself to energy and diffused himself into every living thing on Earth.
On his return in 2018's Uncanny X-Men, he's became arguably Marvel's most powerful example of this trope in part because he got his powers back because of a Life Seed, the counterpart of the Death Seed that made Apocalypse what he is. He's casually capable of erasing every church and holy place on Earth, while simultaneously keeping Apocalypse and Kitty Pryde restrained, and Magneto (among others) on a psychic leash, swats entire teams of X-Men (including the likes of Jean Grey) like flies, and utterly terrifies Legion, a powerful Reality Warper in his own right. He demonstrates just why Legion's so afraid of him by effortlessly flattening Legion, inside Legion's own head, after seeing through the other Reality Warper's illusion and delivering a calmly brutal Breaking Speech and possessing him (all things told, trying to trap the most powerful telepath in the universe inside your own head? Bad idea). He rounds it all off by finally creating the Age of X-Man, a whole new plane of existence, complete with people who're implied to be genuine, living beings, rather than just mental constructs - and while the claim is argued, a striking number of their counterparts turn up on Krakoa shortly afterwards.
Proteus on the side of bad. Fortunately, he seems to have limited range, and limited ability to make permanent changes. If he could, he'd make Emperor Joker look like a day at the park. As he cheerfully asked the X-Men when they found him in Edinburgh, "Have you ever heard a city scream?" Thankfully, he's a reformed character these days.
David Haller aka Legion, son of Charles Xavier, which is actually only one of his Combo Platter Powers, but each comes with him having a new/different alternate personality. Following his mellowing out in the Age of X-Man (where Nate more or less offered to give him the chance to be left alone), he's graduated to a higher level of this and a clearer understanding of his powers.
On the "insane, or is he?" side, you have Psylocke's wacky brother Jamie. He sees the world as a collection of "quantum strings," and by manipulating those, he can manipulate... well, due to Power Creep, Power Seep, it went from "everything around him" (think Proteus) to "everything, period" (think Q.) It's a good thing for all involved that the "mad" Jamie is more of a Bunny-Ears Lawyer who actually knows what he's doing with his increased power. It's also a good thing that he's mostly evolved from a total monster, who trafficked in slaves, into someone who's mostly just annoying.
On the side of whoever's holding them, the Cosmic Cubes. Except for the ones that have evolved into sentient beings, which they invariably do if they last long enough.
The Beyonder is an unfathomably powerful reality warper, just short of Omnipotence. However he was waaay too powerful for his own good. Although he did not know how to defecate until Spider-Man patiently showed him how. Way to take one for the team, Spidey. Beyonder was later revealed to have formed from a not-quite-complete Cosmic Cube... sort of. His origins have gone back and forth a bit, and most recently he's considered a 'child-unit' of the Beyonders, who had to speed run a few stages of his development to regain his sanity. While he's pretty amiable and on the ball these days, he's admitted that he'll always be a little bit broken.
Doctor Doom towards the end of The Secret Wars, which ended up being his undoing, as he was tricked into thinking about scenarios that would bring back his defeated opponents to fight him, thus making it happen. He gains this level of power again by killing the Beyonders and becoming God Doom in Secret Wars (2015), ruler of the fragments of remaining multiverse.
The Molecule Man, Owen Reece, who can manipulate reality thanks to his ability to reshape molecules. This power comes from the missing fragment of the Cosmic Cube that formed the Beyonder, which incidentally left him immune to Beyonder's power. Unfortunately for Reece, he's always had one big problem: a serious lack of self-confidence. When he graduates past that, noting that his old nickname is decidedly understating what he's capable of, even the newly empowered Lifebringer Galactus treads very carefully around him.
In The Ultimates, she once tried to attack Wolverine in the Savage Land and brought the dinosaurs back.
Billy Kaplan, aka Wiccan of the Young Avengers, shares the Scarlet Witch's powers and is the reincarnation of her lost son. His power level is enough to make the Avengers nervous, to the point that Wolverine was willing to outright kill him. Billy's only a teenager, but he's managed to summon and then kill an Eldritch Abomination, and Doctor Strange approached him to talk about the possibility of Billy becoming the new Sorcerer Supreme. It's safe to say that given enough time and training, Billy has the potential to match or even surpass his mother. Which is not even taking into consideration his Demiurge powers, which allow him to pretty much rewrite the entire universe at will. As in, he steps out his universe, onto the page of the comic and starts changing and rearranging panels, which makes him nearly as powerful as the writers. Physical God may not even begin to cover it.
Mad Jim Jaspers from the Captain Britain storyline "A Crooked World" (referred to by other characters variously as "reality butcher", "the Jaspers monster" or "the Jaspers thing") has been described in The Official Handbook of the Marvel Universe as the most powerful reality-warper ever to exist in the Marvel universe because he is capable of affecting realities other than his own. Jaspers is also totally insane and takes to poisoning and twisting reality around him because it seems like good sport. He was only defeated when the Fury, a super-adaptable cyborg created by the Jaspers of another universe transported him to an empty void outside reality where there is nothing for him to control, and incinerated his brain. A weaker Mad Jim from an alternate world was so powerful, his universe had to be destroyed. If the main (616) Mad Jim were to be fully powered, that may not be enough.
Merlyn:This version of Jaspers. Is too powerful, too dangerous. His counterpart could at least be halted, even if it meant destroying his entire continuum. This one is not so easily containable. And if he cannot be defeated, then the omniverse shall fall into chaos, and a new and hostile god shall play dice with matter.
Given that it was made by use of his powers and taking into account its somewhat imaginative attitude to having a healing factor, the Fury might well count as well.
The Impossible Man from the planet Poppup, one of the Fantastic Four's earliest adversaries. He generally only displays shapeshifting in regular continuity. But a very creepy version of him appeared in the Exiles, where an alternate-universe Impossible Man became semi-psychotic due to a botched mind control attempt on him. He turned the Avengers into paper dolls, transmogrified most of the population of Washington DC into glowing butterflies, and didn't realize any of what he was doing — he was just trying to be funny. Thankfully, he managed to undo it all once he broke free.
In X-Statix, Arnie Lundberg was a Reality Warper who, before his Heel–Face Turn, terrorized his home town in a manner reminiscent of "It's a Good Life". Oddly, he could inflict transformations on others, but couldn't fix his own severely scarred face.
In a back-up story in an issue of X-Men Classics, the Watcher speculated that the ability to alter the fundamental nature of reality is the ultimate power of the Phoenix Force. She falls well short of the likes of the Scarlet Witch at the height of her powers in practice. In The Dark Phoenix Saga, Dark Phoenix did destroy a solar system, but it was by using a star as fuel; sucking up part of its energy caused an imbalance that caused a supernova, rather than her erasing it with a wave of her hand or something. She can use her maxed-out telekinesis to rearrange an object's subatomic particles until you get some other kind of matter - she once turned a tree into solid gold easily - and she has power over life and death as part of The Phoenix motif, so she's perhaps on the low end of this list.
It was sometimes implied that Phoenix's power was limited only by Grey's imagination. Dark Phoenix's destruction was somewhat limited by the fact that Jean was fighting against herself. She easily could have killed all the X-Men, but couldn't bring herself to do it. As Phoenix before she became Dark Phoenix, she unconsciously limited her abilities so that at some crucial moments she tried to channel more power, but instead a mental circuit breaker was tripped, shutting off the power completely.
More recent stories involving the Phoenix have shown Jean as the White Phoenix of the Crown holding galaxies in the palm of her hand.
The Sentry started out as a Flying Brick with various other ill-defined powers, but it seems the truth is he has control over matter itself. He killed the Molecule Man in about two seconds and can resurrect himself even after being disintegrated on a molecular level. It's said that if he went completely batshit insane, the Scarlet Witch (House of M and Decimation) would be nothing by comparison. Since when controlled by the Void he levelled Asgard in a matter of moments just through his flying brick powers, this is worrying. Death isn't a solution; at one point, he decided to be dead following a spectacular Trauma Conga Line, got forcibly resurrected, and found no-one knew how to kill him again.
At one point, it was implied that the reason the Sentry has a Multiple-Choice Past is because he's such a powerful reality warper, and has so little conscious control over his powers, that his "true" origin is whatever he thinks it is at the time.
The Ultimate Avengers version of Loki. It seems via somehow tapping into the Odinforce, he is able to do things like change Thor into a mortal form, make himself immune against Mjolnir, change the color of the sky, and teleport a host of monsters, among other uses. The trick is, he can't use it too many times at once or much of it without alerting Odin to it.
The main universe Loki is strongly hinted to be a reality warper as well, but it's not clear if he is aware that he is. While he is a god, the Asgardians (Odin aside) are not generally shown to be omnipotent, most have very little in the way of powers at all aside from vast strength and longevity. Loki gives out powers to mortals like candy, he's altered his own past and the pasts of others by basically creating a retcon in the story, and in the process actually created the goddess Hela (Leah) from nothing, and now he has begun warping reality up to and including creating people subconsciously. It has been confirmed by Kieron Gillen that he has been laying the groundwork for Loki to be a powerful reality warper, and in fact that the entire plot of Young Avengers was Loki's subconscious manipulating events. "In short: Loki’s subconsciousness creates a plan to put Loki in a position where he has to confess or lose. This was all Loki’s plan."
As of Loki: Agent of Asgard we can take it as given that they're fully aware of the extent of their powers, but also the cost of it. In Layman's Terms: According to this series Loki's powers run on the Theory of Narrative Causality (they literally lie things into existence), so if they doesn't tell a passable story, their subconsciousness or the universe will. As they're currently trying to do a Heel–Face Turn this means that they need to learn self-control because taking the easy route with this Story-Breaker Power is a sure-fire way back to Chronic Villainy.
Ultimate X-Men (2001) introduced a Sixth Ranger Traitor in the form of Magician, whose reality warping usually manifested in him gaining new powers constantly and giving him anything he wants. His power also worked subconsciously, creating a fantasy to get him onto the X-Men and passively brainwashing everyone around him in into liking him. After a confrontation with the X-Men, he ultimately fakes his death and leaves them, as his power was uncontrollable by nature.
The Shaper of Worlds could alter reality on at least a planetary scale, but lacked imagination and so had to use others' dreams as a template. (This was because he was an evolved Cosmic Cube. In fact, his true form resembles a Skrull, because that species most often used the Cube he used to be.) He served as a tutor in reality-shaping for Glorian, a human, and Kubik, also an evolved Cosmic Cube.
Anyone who wields the Infinity Gem of Reality has the power to warp reality, though it's not exactly easy.
Then up to eleven when the Reality Gem is wielded with the other Infinity Gems with something like the Infinity Gauntlet.
This includes any alternate universe counterparts, such as the Wishing Cube (made from six planes of forever glass) from the Great Society's Universe.
The ring of the superhero Freedom Ring can manipulate reality within a sphere of a radius of 15 feet, due to the ring holding a shard of a Cosmic Cube. This is a rare case of very limited reality warping, as if any creation leaves the sphere, it fades from existence.
Absorbing Man once used his power to duplicate the properties of a Cosmic Cube. Stuff got very strange when he started punching stuff, like transforming people's costumes into older versions, and splitting the Sentry into the Sentry and the Void. People were mostly just very grateful that he hadn't started thinking about the real potential.
The obscure oneshot X-Men character Mister Marvel put an interesting spin on this. He could alter reality, all right... but the changes to the universe he made were perceptible only to him. In effect, he was living in a fantasy world of his own design. To himself (and only himself) he was the world's greatest superhero; the rest of the world saw him as a frail old man. Then House of M happened, and suddenly he was a frail old man for real.
Doctor Strange at full power can do astonishing things to the fabric of reality, but for the most part he polices reality warpers rather than acts as one himself. This is because, as has been emphasised in recent years, "all magic comes with a price." For instance, after Secret Empire, he successfully resurrected Las Vegas. Unfortunately, in doing so, he raised up a chunk of Hell.
Ms. Marvel dealt with a kid with such powers once in her own series, who was created by an organization of mad scientists who experimented on their own kids in an attempt to recreate the powers of Scarlet Witch because they were impressed with her work creating the House of M.
The Galacta: Daughter of Galactus miniseries suggests that all mutants are actually unconscious reality warpers who alter reality to make mutant powers possible. It's non-canon, but it makes as much sense as any other explanation.
During the Heroic Age storyline, The Hood had the potential to have incredible reality warping powers after he stole four of the Infinity Gems, including the Yellow Reality Gem, in his plan to murder the Avengers out of revenge. However, as Uatu the Watcher noted, while his ability to use the Gems was impressive, he was still limited because he simply thought about using the Gems to enhance his own power rather than really thinking about what he could do with them; he mostly just engaged his enemies in direct combat and never considered just using them to will them out of existence.
Thanos' son Thane can warp reality with his left hand. When he first manifested the power he couldn't control it yet, so he was "only" able to kill everything around him.
Kobik, a little girl born from the shards of Cosmic Cubes that somehow fused together. She's a friendly and cheerful child who just wants to play and be friends with everyone. Including the Red Skull since he was the wielder of one of the Cubes that formed her and she has fond memories of the time they remade the world together.
Sleepwalker is a mild example compared to the humans mentioned above. His Eye Beams are referred to as his warp beams, warp vision, or (as is standard in more recent comics, warp gaze) and their main effect is Voluntary Shapeshifting on anything Sleepwalker chooses to affect with them. For instance, he can twist streetlamps and mailboxes to restrain criminals, turn a window into a slide to save someone from falling to their death, or box in people who are trying to attack him. Sleepwalker can also use his warp beams to project images or to free people from Demonic Possession. While these abilities are powerful, Sleepwalker can't pull off the various feats human warpers can.
Gwenpool has an odd variation in that her power comes from the fact that she knows she's in a comic book and can exploit it to her advantage. It evolves over time from Medium Awareness to this, to the point a future version of herself does it both For the Evulz and to ensure her own existence, causing Civil War III and outing Miles Morales's identity as Spider-Man (which causes the death of his entire family). Gwen vows to never become her which erases her from existence and ends Gwen's comic prematurely.
Extended further in Gwenpool Strikes Back in that she merely can say that something happened before to make it true, which she does with Iron Man who only remembers it after she said it. She also does this at the end to rewrite her own backstory, becoming a mutant, to ensure she won't be forgotten or sidelined by Marvel.
The Inhumans have the Reader, who can make anything he reads become reality, which led to his blindness, as his fellow Inhumans were scared by this people and forces him to use braille tablets to use his power. One of his most notable feats happened while working with Matt Murdock during Daredevil (Charles Soule) to bring down the Kingpin (who became mayor thanks to the events of Secret Empire), when upon reading about Mike Murdock, an identity Matt concocted when Karen and Foggy got close to figuring out he was Daredevil, an actual person.
