Blue Marvel from Adam: Legend of the Blue Marvel gets his powers from being a "living anti-matter reactor". Luckily for him and everyone around him, he's also immune to the effects of this transformation. He also has limited control over the anti-matter he generates, so that he doesn't blow up the city every time he wants to blast a bad guy.
In Avengers: The Initiative, Butterball's Nigh-Invulnerability powers have frozen him in the (quite obese) form he was when they activated, which means he cannot realize his lifelong dream of being a superhero because he can never train and get in shape for crimefighting, and he doesn't even have muscles necessary to fight in a way the likes of X-Men's Blob do. What's worse is that when another recruit with fire-based powers offers to have sex with him (since she risks killing most people), he says that there's no point because his powers also nullify his sense of touch. One of his trainers says that if they stuck him on a low-calorie diet and made him exercise intensively he would probably start to tone up... in thirty or forty years. Of course, the Initiative could use their nanotechnology to block his powers and then train him, but their chief scientist is really a Skrull and he uses his position to kick him out.
In one story set in Cap's early days, it's revealed that when he decided to take up shield-slinging as a method of attack, he had the strength to pull it off, but not the math skills to make it fly true. It took him awhile to do it.
Though this is largely ignored in the comics, the Falcon wears protective lenses in Avengers Assemble and Captain America: The Winter Soldier — the reason, of course, being that given how high and fast he usually flies, his eyes would either become damaged or blinded due to the wind speeds at those altitudes.
Daredevil is occasionally shown having to deal with the sensory overload that comes with his powers, especially regarding hearing and sound. Notable examples are loud sounds or concussive blasts (like from an explosion) disrupting his sonar and causing him pain, and having to sleep in a soundproof isolation chamber.
In Daredevil (2003), he's shown sleeping in a sensory deprivation tank, which closes and opens according to a timer.
In Daredevil (Mark Waid), Daredevil fights Bruiser, who can shift his center of mass to make himself super-strong or make it difficult for Daredevil to flip him. Using his radar sense, Matt can detect that Bruiser's body can't handle the changes to his body made by the power, so he concentrates on one shattering bone and hits it, escaping from Bruiser.
Deadpool's Healing Factor only works because he has such severe cancer that his body is constantly regenerating lost cells. He just makes it regenerate more when he takes damage. He actually weaponizes this when the Skrulls want to make an army of clones with him, and gives them the healing factor, but not the cancer, causing them to mutate and die.
However, while he has to ability to regenerate tissue, there is no guarantee that it will regenerate right. Once he broke multiple bones and his assistant strapped him to a rack in order to ensure that they would heal straight.
The Eternals are powered by cosmic energy flowing through every cell in their bodies. This makes them able to do things like fire Eye Beams and use Super-Strength, as well as powering their Psychic Powers, but dispersing all the resulting waste heat is quite a problem — they tend to stick to cold places like mountaintops and the middle of Siberia for just that reason. Gilgamesh even went into a coma once fighting a lava monster — and before that, he had to go into a motionless trance just to survive in a hot cavern while guys like Captain America and Black Panther just stood around and sweated. The laws of thermodynamics are a harsh mistress.
The Human Torch has the fireproof skin/lungs/etc. secondary power. In a Fantastic Four: World's Greatest Heroes episode where he swapped powers with his sister, he tried to eat pizza straight from the oven and exclaimed "It bit me or something!" When Sue tells him it was just too hot, he says "Oh, yeah, I remember that."
The Invisible Woman's force-fields aren't permeable to air, and the limited air supply is used both offensively and as a limitation when she's using it for protection. Like nearly everything, this is Depending on the Writer.
In Marvel Adventures Fantastic Four #26, the Silver Surfer reasons that she can make her force fields porous enough to allow air for her to breathe. He takes full advantage of this when he defeats the Four by overloading their powers, causing her to nearly suffocate.
Sue's invisibility is explained as such: she extends a light-bending field around herself and her immediate area, which is what renders her body and clothing invisible, and she can extend this to other people or objects if she wishes. As for her vision, remember that she can see other things that are invisible — whether it's under her power or not. Her eyes can perceive wavelengths of light that normal humans can't, and it's through these wavelengths that she can see while invisible. (Though this still doesn't explain how other people can still see when she makes them invisible.) Again, Depending on the Writer.
When Stan the Man created her, he might have remembered that Marvel had already done this story in Tales to Astonish earlier the same year, lampshading this problem with invisibility. Maybe if he had we wouldn't have all these Flame Wars today regarding Sue's eyesight.
In fact, the original letter that detailed the Fantastic Four and their powers was reprinted some years back in a special issue. Sue's eyesight is not mentioned, but she was permanently invisible and unable to make anything else invisible, even clothes. This was nixed because Sue taking off her clothes on-panel was deemed too sexy.
Chamber from Generation X is a triple subversion: he doesn't need to eat, breathe or drink thanks to the pure-energy furnace within his chest, which is a fortunate thing since the same furnace blew off his jaw and a good portion of his chest when his powers first surfaced. With no lungs or mouth, he can't talk normally but then he develops a secondary mutation of telepathy to communicate with others. As it turns out, he doesn't need telepathy; he has the potential to reconstitute his missing parts but isn't skilled enough in his powers to do so for long. He nearly died in Decimation when he lost his powers and suddenly needed things like food, water, and oxygen again.
Red Hulk from The Incredible Hulk becomes hotter the madder he gets, allowing him to burn and melt things just by touching them. He suffers his first defeat when he becomes so mad that his own heat hurts him.
Played straight with the character Misty Knight in Iron Fist. She received a bionic arm after losing one in an explosion. While she can use it to deliver a hard punch and has a crushing grip, whenever she tries to use it to do something her un-augmented body cannot handle, it causes her considerable pain and she has to quickly dial it down to prevent injury.
Iron Man villain Ezekial Stane, the so-called "Iron Man 2.0", has bioengineered himself in such a way that he can fire repulsor blasts using his own bioelectricity, increases his healing, and so forth. However, he has to consume a very high calorie paste in order to keep his blood sugar up, and his armor chiefly acts as a way to vent heat from his body, as he hasn't figured out how to keep his flesh from burning off.
During one Moon Knight mini-series, the titular character has bracers with retractable claws made for him so he can mimic Wolverine's fighting style. When he asks whether these claws are made from unbreakable adamantium like Wolverine's, he is told that would be pointless, as even with plain high-tensile steel his arm would break long before the claws do.
The New Universe paid a lot of attention to this trope, as part of its pitch of being more realistic:
Minor villain Skybreaker could fly, but had no other powers, so he required a special suit to protect him from wind, friction, high-altitude cold, and to provide oxygen. It also has navigational gear, since there are precious few road signs at 40,000 feet.
D.P.7's Jeff Walters (aka Blur) was a super-speedster who did require large amounts of food every day. He was also obese before his power manifested via the "White Event".
Food was the lesser problem. Apparently, his body is potentially much faster than his mind, so he can't get a restful sleep if not under tranquilizer (or a teammate's energy draining power). And the constant vibration caused by lesser muscular movements cause him to be mildly destructive when touching things. Or opening Coke cans.
In one issue of The Punisher 2099, the Punisher tracks down a techno-shaman who has encased himself in an impenetrable force field to protect himself. Punisher figures out that it still has to be able to exchange heat through the field, and fries the guy inside the force field by showering it with hot plasma.
The Marvel-616 version of Quicksilver once remarked that his body efficiently processes all his food, giving him the energy to run, and that his feet are designed to withstand the impacts of repeatedly hitting the ground. Pietro's enhanced physiology also gives him Made of Iron qualities and makes him far more durable than he looks, as a body capable of withstanding the stress of traveling unprotected at the speeds he hits would need to be immensely tough. This frequently comes up when he's attacked by someone who assumes he's another Fragile Speedster only to be surprised when he shrugs off what should be a devastating blow. He also has the Required Secondary Power of super-perception, and while he can slow it down as he speeds up, his default is still faster than human normal. It's described as the reason that he's so aggressive: everyone else to him "is like standing behind someone who doesn't know how to use an ATM" every single moment of the day.
Ruins plays with this creating a Death World where nobody has these. This story is the logical extreme of every character having only their primary powers and nothing else to make those viable or safe as gamma radiation turns Bruce Banner into a green pile of tumors, Peter Parker develops a deadly viral rash from his spider bite, Wolverine is allergic to adamantium, and the Fantastic Four end up becoming grotesquely misshapen corpses.
It's possible that Spider-Man's super-strength is a Required Secondary Power. Everything else —agility, wall-crawling, advanced nervous system— falls under "proportionate powers of a spider" but spiders aren't really known for their brawn. It does, however, probably keep him from dislocating his arms when he leaps from a great height onto the side of a building.
Spiders, like ants and many other insects, have a muscular system that is actually built on the same principles as hydraulics. How Spidey pulls off hydraulic-based strength without massive physical mutation, however, is anyone's guess.
Lampshaded on at least one occasion when Spidey loses his powers but still has his web shooters; he tries to swing away but lacks the strength to hold onto his own web!
In Ultimate Spider-Man, since the "radioactive spider" is changed to a spider with an experimental retrovirus, his powers aren't anything to do with the spider at all — they're side effects of enhancements that the lab was trying to make to a spider. Spiders don't have a 'spider sense', for instance, which is the required secondary power for all of the things he uses his strength and agility to do.
Non-organic webshooters require him to have the chemical and mechanical engineering skills to build them. In The Amazing Spider-Man, the fluid is organic, just compressed, and he builds a way to deploy it. In some versions, the formula came to him as part of his powers.
Spider-Man's Spider-Sense gives him a mental understanding of his immediate surroundings, not only for predicting danger but for placing his webs while swinging through New York's skyline. On occasions where the spider-sense is disabled by outside sources, he notes that he never put much thought into it since the calculation of where to stick his weblines to had always been taken care of for him, and that he'd never looked both ways when crossing the street since the day the spider bit him. As a result he had to slow down dramatically to make sure the points his webs connected to were stable, because a loose/weak structure could give way or break under his weight and send him falling earthward from several stories up.
His fighting style was also completely dependent on his spider-sense until it was nullified, making him far less effective in a fight without it; since his prior style was to basically use it to be where his enemy's fists weren't and then hit back when their guard was open. It took lessons from Shang-Chi for him to develop his own martial art, "the Way of the Spider" and restore much of his effectiveness. Then he got his spider-sense back, now backed up by genuine fighting prowess...
Spider-Man's sticking powers are sometime shown to be limited by the material he sticks to. Sure, his power to stick to objects is powerful enough that it takes the strength of the Hulk to directly overcome it, but much weaker villains have managed to pull Spider-Man off of walls by pulling the parts of the wall Spiderman is sticking to with him.
One that's rarely, if ever, commented on is how much time Spider-Man spends upside-down without suffering from any of the effects of blood rushing to his head as a regular person would.
In a Spider-Man comic in which Doctor Strange's mansion is destroyed, there are these floating masks (they have something to do with Cyttorak) who can "wear" human faces and fire laser beams while doing so. Too bad they can't sustain the bodies...
The Sandman can control his own sand, making it fly and move around, including turning himself into a cloud and controlling his own direction of flight (so he's not using the wind), so Sandman clearly can fly.
Subverted by Spider-Boy. Bailey complains that all of the blood is going to rush to his head when Peter webs him to a wall upside-down. Peter remarks that the other spider-heroes don't have this problem, showing how different Bailey's powers are from Peter's or Miles'.
Taskmaster can achieve limited Super-Speed if he copies the moves from fast-forwarded video, but he can only use it in small amounts, since he does not have secondary powers to compensate for the fact that it strains his body.
He also lacks certain required secondary skills — for instance, when he was young, he copied a professional diver's dive. But neglected to learn how to swim first.
Taskmaster is a bit of an odd case; he supposedly has no superhuman powers beyond his signature "photographic reflexes", yet is not only able to pull off the aforementioned feats, but also Spider-Man's speed and agility, and further, can catch bullets, leap dozens of feet vertically, casually send a man flying with a punch and shake off getting smashed through a reinforced wall by the force of an enraged Spidey (thinking Taskie had kidnapped Mary Jane) kicking him in the head.
Eventually, it was shown that every time Taskmaster memorizes a new set of moves, he loses a bit of memory, including things like his real name. While this isn't how memory works, it may explain why he's able to do Spidey's moves. If his brain is constantly compartmentalizing, it may be able to shut off the parts of the nervous system that would cry out in pain when attempting a crazy maneuver, while increasing adrenaline output (á la mothers lifting cars off of their children).
Reed isn't even strictly human anymore (to the point where he doesn't even need to eat), as his organs have been replaced with a hyper-efficient bacterial stack that bends and twists with his body.
Johnny is a living nuclear reactor that achieves perfect fission using his body's fat cells (which gets him into trouble, as he initially doesn't eat enough to support his powers and ends up in a brief coma because of it).
Ben is literally the Ultimate Life Form, with limitless strength and the ability to survive any environment... but the adaptation to do so means that his body obeys the Square-Cube Law and is super-dense as well as incredibly large (nine feet tall and in the neighborhood of eight tons), which is why his craggy "Classic Thing" appearence looks the way it does.
Sue Storm lampshades the impossibility of her powers, pointing out that there's no conceivable reason why she should be able to see things while invisible. Luckily, she's a bio-geneticist and thinks the mystery is fascinating.
In The Ultimates, mutant super-speedster Quicksilver has a Required Secondary Powers battle against Hurricane, an enemy speedster who'd got her powers from advanced surgery, and who wears a reinforced suit designed to resist friction. He grabs her and starts accelerating. Her skin bursts into flames around Mach 4 or so, and she completely disintegrates moments later. So much for the suit. Quicksilver, whose mutant power includes all required secondary abilities needed to move at an acceptable fraction of the speed of light, reminds her smoking body that he'd been easily hitting Mach 10 since he was a teenager. The moral of the story: if you fight someone with the same primary power set as you, make sure your Required Secondary Powers are up to their standard.
Colossus can turn his body to steel. It was later revealed that he has no natural super strength to compensate for the added weight of a metal body and instead dopes with a power-magnifying super-steroid. The Ultimate Galactus Trilogy also has a bit when Sam Wilson realizes that if Colossus turned his entire body to organic steel, then he wouldn't be able to see. One eye poke later...
The Unbeatable Squirrel Girl has retractable spikes hidden in her knuckles similar to Wolverine, but rarely uses them. For one, she's not really interested in stabbing people, but also because she lacks Wolverine's healing factor. Getting the blood of whatever mutant, monster or even regular human she's fighting into her system without it would be unhealthy.
One arc in her solo series sees her fight a villain who can split himself into multiple smaller copies; these copies can also merge themselves together to become a giant version of him. However, unlike similar growing/shrinking powers in the Marvel Universe (such as Pym Particles), his powers lack the ability to let him defy the Square-Cube Law; as such, Squirrel Girl is able to incapacitate him by tricking him into going into giant form, resulting in him injuring himself.
When John Byrne took over writing and drawing West Coast Avengers, he came up with the theory that the probability-altering powers of the Scarlet Witch must actually require the power to rewrite all the history that goes into creating probabilities, thereby turning her into a Reality Warper.
Some of Wolverine's secondary "powers" have been indicated. When Rogue got a full taste of his Super-Senses, she was overwhelmed by the sensory input (and in intense pain, as the tactile sense was in overload as well; his use of meditation apparently helps him deal with it, along with constant exposure to mild-to-excessive pain giving him a very high threshold for pain, and it may also explain why he always seems to be in a bad mood and how, though he can survive it, he doesn't collapse whenever he takes a few hundred rounds to the chest and face). The problem of why the backs of his hands, where the claws come out, don't each have three holes is explained by his claws actually punching a hole through his flesh every time he extends them, at which point his Healing Factor closes the wounds before he bleeds all over the place. Just where all the mass of his body comes from when he heals from massive injury (for instance, all of his organs and flesh tissue, aside from his brain and skeleton, more than once), however, is completely ignored. As is why his bones don't fall apart when everything that's not bonded with adamantium is completely destroyed. He does tend to wind up naked when that happens, though, at least.
It isn't completely ignored, actually... it probably wasn't Claremont's, but there was a short arc in which Logan, while traveling through a desert, catches and eats raw a crow (he feigns fainting to let the birds approach) after a hallucination he was having (long story) reminded him that his healing factor needed proteins in order to regenerate tissues. For regeneration of far more severe injuries, another explanation has been given in another comic: Logan had... ahem... defeated the Angel of Death in a duel (he didn't know who the guy was though) and had since then been granted a sort of "immortality" (his healing factor was able to heal him from any injury). At the end of the arc, Logan had his "pact" with the Angel canceled and was informed that, from that moment on, his healing factor was going to be far less effective.
He's got to have superhuman strength (or close to it) to be able to be agile at all while carrying around a skeleton that weighs around a hundred pounds, Depending on the Writer, more than a normal human's. Possibly the result of his healing abilities building more efficient muscles, since he was pretty quick relatively shortly after receiving his adamantium, or a combination of that and training while lugging around so much weight.
In a What If? story in which all superheroes and villains lose their powers after M-Day (rather than just the least marketable mutant characters), Wolverine lacks the strength to move with his adamantium skeleton and is effectively paralysed until Tony Stark builds him an Iron Man armor to allow him to walk. No explanation for why the massive metal poisoning doesn't kill him, though.
One description of his healing factor indicates that he has unlimited stamina — due to constant regeneration, his muscles never tire from overuse. Thus, Wolverine is granted a degree of superhuman strength from constantly training and fighting with 100 extra pounds of adamantium to haul around. Also, human muscle is much stronger than one might think, but using it to its full potential would result in muscle damage and liquefaction. Wolverine's healing factor means he can use his maximum theoretical strength all the time. Combined with unbreakable bones, this means Wolverine can also lift objects much heavier which a normal human otherwise could with their own muscle strength at peak athletic levels, but cannot in reality due to their bones snapping from the pressure.
Wolverine's healing factor even extends to his mind. As stated in the trope description, super-healing doesn't account for a mind being overloaded with pain. Wolverine's healing factor, however, compensates for this by cutting out the most traumatizing memories (both emotionally and physically). This can be interpreted as meaning that the reason Wolverine is able to withstand such devastating injuries because his brain cuts out all trace of the trauma, much the way the brain in Real Life averts Dizzycam by inducing temporarily blindness whenever the eyes move.
This has been given as one possible reason why he will never fully recover the memories that he had before his adamantium implantation: his healing factor is preventing him from recovering those memories because they would be too emotionally painful.
Despite the "protein" point above, he once survived, when trapped under a glacier for six months, by eating parts of himself.
Alternately, the lack of hayflick limitations could be part of his primary power (the telomeres simply heal like everything else instead of degrading with divisions), which would make the required secondary power some sort of alternate storage mechanism for the information in his DNA, used to repair that DNA when damaged.
Death of Wolverine points out that, without his healing factor, the simple act of using and then retracting his claws would likely give Logan a lethal blood infection.
In the 2021 Avengers: Tech-On limited series, the Red Skull manages to strip the world's superheroes of their powers. Logan immediately collapses in utter agony, with Shuri pointing out that his body can't handle the adamantium on his bones without the healing factor there to compensate. She further explains that even with Wakanda's advanced medical technology, any surgical procedure to remove the metal from Logan's skeleton without an active healing factor would most likely kill him.
The simple existence of Logan's Healing Factor is this: once someone stopped and realized what would actually happen to someone whose entire skeleton was covered in metal, his healing abilities were invented to explain why he was even still alive. As a result, whenever Logan's healing factor isn't working, he faces a slow death from adamantium poisoning without medical intervention.
Chris Claremont usually averted this, giving the X-Men their Required Secondary Powers explicitly and having some of them learn to use them on their own. However, he wrote one of the junior team, Sunspot, as super-strong but not invulnerable, which led to a letters-page discussion about why the character didn't break bones while lifting things.
Banshee's hearing is extremely powerful. According to him, with powers like his (Super-Scream), the alternative would be being deaf.
Angel/Archangel has the increased strength and stamina necessary to fly with a gigantic honking wingspan. His wings themselves are also strong enough to slap a grown man across a room, or break many bones at once.
His actual wing surface area isn't nearly large enough to lift a human-sized body using real-world physics— ever wonder why hang gliders are so big? So Stan Lee gave him a required-power weight loss by attributing zero body fat and hollow bones like a bird— except that doesn't work out either, the largest birds have proportionately a lot more bone per body volume than even the smallest human, let alone a six-footer like Angel, and hollowing his bones only shaves off a few pounds of weight. Likewise, a man of his athletic build and muscle mass normally has less than ten percent body fat anyway, not nearly enough savings in weight, especially with such a high proportion of dense muscle.
He also presumably has a more efficient oxygen absorption system (birds have vastly superior lungs to mammals), although it is never stated
One power of Archangel's that seems to come and go Depending on the Writer is that his blood has healing properties, meaning he is able to grant people a temporary healing factor through a transfusion. He is not a universal donor and does not have an unlimited amount of blood, so there are limits on who and how many he can heal.
Along with his super-efficient lung capacity, his tolerance to extreme wind conditions and cold at high altitudes (he's been shown casually hitching rides on airplanes for long distance travel and having no problems with the thin air, cold, or high velocity airflow) also ends up forgotten by many writers. See below.
The secondary power of "can tolerate cold temperatures" is memorably played up for three X-Men at once in an issue of X-Men Unlimited, while a team of Storm, Iceman, Colossus, and Angel are on a mission in Antarctica:
Storm: Hmm. Angel, my weather powers protect me from the chill, Colossus is immune to extreme temperatures while armored, and Iceman is, well, Iceman. How are you doing? Angel: I'm very cold, thank you for asking!
This is a bit of research failure regarding Angel, since he's adapted for extreme heights that actually includes an ability to handle frigid temperatures (see above), though it's not specified if there's a difference between the temperature at altitudes he's used to flying through and the temperature on the ground at that time. It's possible that his tolerance to cold was just overcome.
Kitty Pryde apparently cannot breathe while phased (because the air is out of phase with her), let alone breathe when inside solid objects, and yet for some reason can still walk (and not drop straight through the center of the Earth whenever she phases), presumably because she can create some sort of phase boundary between the soles of her feet and the ground that allows the ground to continue to hold her up against gravity. This was entirely implicit until Grant Morrison's run, when for instance, Kitty can often be seen climbing air (using the same boundary effect) and can breathe while phased in open air at least (because she can phase the air around her the same way she phases her clothes or people she is holding.)
A similar assumption can be made that Nightcrawler can extend his teleportation outside the limits of his body: if he didn't, every time he used his power his clothes would drop off. Since he can take another whole person with him if he is in direct contact when teleporting, this seems to be fairly plausible.
According to The Physics of Superheroes (by real-world physicist and comic book fan James Kaklios), Cyclops must also have super strong neck muscles, as the beams are described as concussive force — without such musculature, Newton's 3rd law says his neck ought to be snapped every time he uses his powers.
The Word of God is that he feels no recoil at all, since the "push" for his eyebeams actually comes from another dimension. He's just the doorway for the particles that make up the beams.
Of course, the first time he activated his powers was to use the recoil to slow his and Alex' descent to the ground from the plane they jumped out of.
Alternatively, there is a minor meme going around which proves Cyclops can fly. The eyebeams produce kinetic kickback, but he is immune to this kinetic energy. If he only held his hand in front of his eyes, then WHOOOOSH.
Pyro of the Brotherhood of Evil Mutants can only control fire, but needs a special suit to generate flames (which is likely also fireproof).
Another X-Men subversion: Armor is a force field-user whose force field is invulnerable to most forms of physical and energy attacks but vulnerable to lasers specifically because it has to let light through. Incidentally, someone once tried the same trick on the Fantastic Four's Sue Storm — once.
Also subverted with Firestar. Unknown to her at the start but unlike many other people with radioactive heat powers, Angelica isn't immune to her own powers and got cancer from exposure to her own output. After successfully being cured of the cancer, Henry Pym developed a special radiation dampening suit for her.
Storm's lightning bolts don't come from her body's own internal energy supply, since she'd have to constantly be scarfing down food just to make up for the calories she'd lose every time she used her powers. This means she's either drawing electricity from the air around her, or is simply generating it from out of nowhere, both of which are extremely impressive. Once again, Depending on the Writer, certain series have specifically stated that Storm actually pulls weather from the surrounding areas in a form of Equivalent Exchange. When she made it rain for her village to experience a bountiful harvest, she put other portions of her homeland into a drought. How far this sphere of influence extends is anyone's guess, though.
As noted above under Angel, Storm has a vaguely defined resistance to effects of extreme weather. This includes at least being able to tolerate extreme heat and cold, and being able to anchor herself in place while hurricane winds are blowing all around her.
Mystique can copy the appearance of other people down to fingerprints, voice and retina patterns closely enough to pass biometric scanners. In addition to the Photographic Memory required to remember all this perfectly, she must have some kind of ESP to detect such things in the first place just from a brief encounter. She's certainly never shown scanning and studying the retinas of people she is going to copy. It's shown in her side series that she requires a minimum of eight words to adequately mimic someone's voice. How this allows her to pick up speech idiosyncrasies is anyone's guess.
This is actually a plot point in the miniseries Worst X-Man Ever. Bailey Hoskins is a mutant with the ability to blow himself up. That's it. That's his only power. What he does not have is any of the powers required to actually survive or reconstitute himself afterwards. If he were to use his power he would be Killed Off for Real.
Implicitly acknowledged with the "Decimation" arc after House of M, as several mutants keep their primary powers but lose the secondaries. Mutants with fire abilities are no longer immune to their own flames and incinerate themselves, a dragon-like mutant falls out of the sky because his mass can't stay airborne under normal physics even with the wings, a fishlike mutant drowns because his gills can't extract enough oxygen from the water to support a human body, and so forth.
The miniseries Galacta: Daughter of Galactus suggests that the mutant gene does not actually confer superpowers on people but, as a result of extensive engineering by the Celestials, alters reality to make mutant powers possible, thereby making every mutant a low-level, unconscious reality warper, handwaving every impossible thing that mutants do.
Quicksilver's sort-of-nephew, Tommy/Speed of the Young Avengers, got a job assembling circuit boards at super-speed at one point. He chugs some coffee, turns into a blur, and then tells Prodigy that from his perspective that was about a week.
The Two-Gun Kid had recurring villain Hurricane (real name Harry Kane). A small-time outlaw, he drank a potion created by an Native American medicine man that granted him a lightning-fast draw and the ability to run faster than a pronghorn antelope (roughly 50-55mph, faster than a horse). However, he quickly learned that he had the speed of an antelope but not the stamina, so while he could outrun a pursuer on a horse for a short time, eventually the horse's greater endurance would win out.
