We've collected all the in-depth information you've ever wanted on how Required Secondary Powers should physically affect various superpowers. But first... Superpowers In General - Most portrayed uses of super-powers have No Conservation of Energy; whether strength, speed, energy blasts, etc., supers tend to use far more energy than a human metabolism can provide. To use any physical power at anything above a moderate level (think Buffy, not Hulk), there needs to be not only access to some source of energy (Another Dimension being the common Hand Wave), but also some means of channeling it through the body's fragile systems safely. Otherwise your characters will be limited to only-slightly-greater-abilities-than-the-best-humans superheroics.
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Eye Beams - Thanks to tiny involuntary movements of the eyes called microsaccades, accuracy and precision would be a problem, which gets even worse the greater the distance of the target. And could result in tremendous collateral damage. So the ability to keep your eyes perfectly still is very important when it comes to fighting crime.
Flight - Other than those with obvious mechanical (or otherwise) assistance (either wings or rockets), flying characters possess the ability to propel themselves through no effort of their own. This might be due to some inherent telekinetic ability, or perhaps it might be due to the ability to manipulate their own personal gravity; in both cases, they probably use some sort of Reactionless Drive. Winged flyers don't have it much better; they need some way to offset the mass and awkward shape of the human body, whether it be super-powerful wing muscles (and more importantly very large wing surface area, about that of a hang glider would do), a bird-like hollow bone structure (which would only save a few pounds for something with the body mass of a human - some engineering doesn't scale up well, as the ostrich can attest), or perhaps even a method of non-powered flight or levitation that is merely augmented by the wings (or some combination of the three). Also, for those that go high into the atmosphere, they also have a reduced requirement for oxygen. As there is less atmospheric pressure higher in the atmosphere (one's lungs operate by manipulating internal air pressure to move air into and out of the lungs), flying characters would either need to stay closer to the ground, be able to generate a higher partial pressure of oxygen from their surroundings (via air-related powers or molecular control) or possess less need to breathe (and thus could stay high up for long periods of time). Presumably, this would also lead them to hold their breath longer at sea level, but even if they can breathe if they have winged-based flight a lower atmosphere pressure would mean less lift so they would need very big wings in order to reach high altitudes. Thirdly, there is an issue of temperature. The adiabatic lapse rate is (in layman's terms) the rate at which the temperature decreases as you go higher above the earth's surface. A flier must have some way of preserving body heat at altitude or they would freeze in short order. Additionally, the speed of flight will cause the rate of freezing to increase, as Space Is Cold will tell you. You'll also be a greater conductor of electricity the colder you get, so that requires some resistance to that. Some of the same problems associated with speed also apply to fast fliers. Flight almost invariably involves a combination of Super Strength and the ability to ignore aerodynamics, as fliers often lift off while carrying someone or something. One also has to wonder how they don't destroy half the atmosphere flying that fast. The shockwave and heat would be devastating - Tunguska style. In addition, it has been pointed out that many fliers must also have some regenerative powers. Otherwise, the constant effects of the wind and airborne dust particles on exposed skin would cause premature aging. Storm for example explicitly has physical resistance to the elements and temperature extremes. Otherwise she'd have skin resembling leather and more wrinkles than women decades older due to constant exposure to fast moving wind, rain, and snow. Fliers with invulnerability get a pass, but that's it. On a related note, there must be something special about fliers' hair, otherwise most of them would be sporting horribly tangled locks after each flight. Even more impressive is the way it never seems to be blown into their eyes (though many female fliers wear a headband for this exact reason).
Invisibility - Applies not just to you, but to things you are carrying, or wearing. Any dirt on you becomes invisible, and either you get clothes made of some suitable material, or provide some Fanservice. Also, your light distortion fits that of your surroundings, and food remains invisible through the digestive process. Also, to use an eye normally one must at least have a lens bending the light (thus being visible at least as glass-like objects), pigments in sensitive cells absorbing the light (as opposed to passing right through just like, say, x-rays) and something preventing the retina from blanket exposure by light not focused with the lens, that is, blocking all the rays not coming in via the pupil, including those from behind the retina. Oh, wait, doesn't that add up to almost a complete eyeball? All of which really raises the question, what counts as an invisible person's body? Just his own cells with his own DNA? Then what about the bacterial colonies in the intestinal tract? What about the mitochondria in each cell, which have their own DNA? What about the lifeless liquids such as stomach acid and fluid in the eyes? What about dead cells, like hair and fingernails? Or the entire outer layers of skin, for that matter? Some Invisible characters can extend the light-warping field over whatever they touch, eliminating some problems but adding others— conscious selectivity is required, otherwise if they bump into something, that item might blink in and out of sight, making them fairly easy to track, especially crossing a crowded room. The issue of how large an object their field can cover also comes up in many continuities. Invisible Streaker is usually the result of lacking these Required Secondary Powers. A standard aversion of these required secondary powers is psychic invisibility, which is a mental or hypnotic effect that causes everybody to ignore you. The upside is that this automatically also foils hearing and smell; the downside is that it tends not to work on cameras.
Rubber Man - Flexing yourself into cartoonish shapes would be great fun, provided you were strong enough to support yourself enough to stand up. There's also the issue of organs and blood. Aside from the obvious repercussions of flattening yourself against a wall, the human heart isn't designed to pump blood into an arm that just grew one hundred feet. This power would also have to extend to their clothes, otherwise it'd be very uncomfortable (or publicly embarrassing).
Shape Shifters - Characters that shift into other objects also have the ability to ignore how said objects would ordinarily hurt people. For example, someone who could become living flame is also immune to being burned (either by their own flame or that of others). Someone who can turn into water often gains the ability to breathe in water (or has no need to breathe at all). Most shape shifters would need an eidetic memory to convincingly imitate every detail of a person they've seen once. Or an encyclopedic knowledge to remember the details of a multitude of objects. This is more commonly averted, as they are just as frequently exposed as fakes because of such a flaw in the disguise, or they are copying someone they are fairly familiar with, or they are even not copying anyone and just using their imagination. There's also the issues of surviving while transforming and in the transformed state (altering one's body structure even a little is usually fatal in the real world, let alone having your flesh turned into another substance or turning into something with no internal organs) and keeping the ability to shape shift rather than transforming into something cursed with permanent Shapeshifter Mode Lock... This one could fill a page on its own. There's also the question of how a shape shifter continues to think (or control his or her own biology) when the brain itself is altered in shape or chemistry. And of course, if the shape shifter can also change his mass... Also, some shape shifters have the power to vanish their clothes into the ether, and retrieve same when they become human again. (Most common when the work is aimed at younger audiences.)
Size Changing - Being able to shift one's size, or even just being differently-sized by nature, has its benefits. However, in addition to the Shapeshifter Baggage question of 'Where is the extra mass coming from/going to', size shifting involves a lot of its own required secondary powers:
1) It would imply an ability to change one's mass so that one does not blow away or sink into the earth (due to the shift in surface area and pressure).
2) Because of the Square/Cube Law, one would need Super Strength to be able to support the increased weight, as well as the increase in pressure on the body. For example, if one were to go from 5 feet to 50 feet, the result would be a thousandfold (10^3) increase in mass and therefore weight, but only a hundredfold (10^2) increase in surface area, thereby increasing the amount of pressure on one's body (or force per unit surface area) to ten times normal. Go big enough and you'd likely barely be able to stand, let alone fight.
3) One would also need the power to vary one's internal body temperature to avoid freezing to death at small sizes, or dying of heatstroke at large sizes (get ten times bigger and the increase in mass will cause a thousandfold increase in heat generation, but the increase in surface area will only increase the rate at which you dissipate heat by one hundredfold). The overt ability to survive a superhuman range of temperatures would also solve this problem.
4) The ability to adjust the performance of your vital organs to accommodate your body would help as well. For instance, a heart in a fifty-foot-tall body requires quite a bit more strength to generate the hydraulic force needed to get blood to the brain, and red blood cells that grow to ten times their ordinary size had better be able to carry far more oxygen than they do at regular size.
Defense, Immunity, and Healing
Force Fields - Force fields are often air-permeable, which not only allows people to speak and listen through the field, but it also allows oxygen to filter in through the force field and thus allow breathing. However when a force field is used to keep water out while underwater, the force field often appears to have the power to actually extract breathable oxygen from the water around it and remove carbon dioxide from within it. This is sometimes averted, and a non-permeable force field can actually be used as a weapon to choke foes. Similarly, they are usually invisible (or at least translucent) until something pushes against them, which means they let at least one wavelength of light (if not the whole spectrum) pass through unimpeded while still keeping lasers or any other emission that the force field's generator considers "harmful" outside. There is also the matter of the energy that is distributed over the field. Something that pushes against a force field is exerting pressure, whose energy has to go somewhere. While physical barriers absorb such pressure by spreading its energy across their structure, or by transforming it into potential energy via elastic buffers, a projected, free-standing force field has no anchoring, and often no elasticity, so it must be dealing with distributing the force inflicted upon it in some way. Otherwise, if this energy were simply "done away with," there would be no reason for artificial or magical fields to buckle under assault at all. This often leads to a character suffering a Psychic Nosebleed as a way of showing his or her effort against such force, implying that the force field is braced against their brain. Ouch.
Healing Factor - Any character with a healing factor presumably also requires superhuman pain tolerance, to avoid falling unconscious from the crippling pain and then waking up ten minutes later good as new. Still would be useful, but not so much in a combat situation (where being unconscious makes you useless at best, and makes you a liability or opens you up to a Coup de Grāce at worst.) It's not really necessary to make the power work, though, so not actually a required secondary power, and there are many examples of healing characters who don't have abnormal pain resistance. More importantly, they'd burn up a lot of energy accelerating the healing process that fast, and so would need super-stamina and more efficient internal energy use than normal (or an alternate energy source) or their own power could kill them by draining their body's resources too fast. And to regenerate takes mass, so either they have limits to what they can regrow at one time, or access to some other source of mass, like Another Dimension— see Shapeshifter Baggage. Also, they'd need a way to fight infection and other foreign substances. Having your guts spilled all over the floor would open the door to all sorts of germs and viruses, not to mention dust and such. There's a reason hospitals strive for perfect sterility. Conversely, they get infected like anyone else, but recover instantly due to the healing factor producing antibodies at an accelerated rate. That in turn would need another secondary power to prevent cytokine storms destroying the body. Wolverine's healing factor was used to develop antibodies to a deadly virus on at least one occasion. Most likely they would also have some kind of super-genome, considering that so much rapid healing and DNA replication would increase the possibility for cancer-causing genetic defects massively. This would explain Deadpool's Massive scarring, since his skin is both spreading the cancer and healing the damage caused by the cancer. And, cancer aside, certain kinds of attacks could reasonably be assumed to cause genetic damage to the tissues which the regenerating tissue is growing from. In addition to that, it is possible that such a healing factor would have to display some sort of Morphic Resonance (or at least be controllable). Having broken bones heal almost instantly sounds much less impressive when you realize that this gives almost no time to set the bone before it heals crooked. On top of that, if you got shot you would have to take the bullet out yourself to prevent eventual lead poisoning, then wait for it to re-heal. Ouch. On the other hand, the healing could be "smart" enough to set bones correctly and start from the inside out so that the bullet is pushed out. Let's not forget when things that are wrong with your body heal as they were. Deadpool gives us a pretty bad look at what happens when your healing factor heals cancerous cells or brain abnormalities as if they were normal healthy cells. Finally, for a human to function normally, you'll need more than just your own cells replaced — there's lots of microorganisms that are important to survival. Just had your guts torn out and planning to regrow new ones? Well, unless you're also spontaneously re-creating bacteria there too, you'll have problems digesting future meals.
Immortality/Agelessness in its various forms - This one is obvious. You're simply in some way exempt from being tied to the normal mortal coil. You're either fully immortal, reincarnated immortal, or ageless but vulnerable. The latter type requires a lot of intelligence and careful planning if you don't want to be discovered. You should ideally have a lot of resources financially, and certain contacts, like people who can change your identity. Also it helps to be VERY mentally resilient, because We Are as Mayflies and so forth. There's an eternal life that does not include eternal youth, leaving you in worse shape every year but knowing that your condition has nowhere to go but down. And then there's the whole "can be mutilated horribly or torn apart but not die from it" scenario, often the result of an careless wish from a Literal Genie, leading to A Fate Worse Than Death, often followed by And I Must Scream as you're reduced to a mangled pile of still-sentient ground chuck. This Cracked article points out the human perspective on time as you get older, meaning that everything becomes inconsequential the older you get, including relationships. And even if you're fortunate to avoid all of the above, you will get cancer at some point down the road. If you are both immortal and invulnerable, you will survive events such as the eventual death of the sun and be floating in space, unlikely to ever see another object again, and never dying, not even of starvation, dehydration or exposure (but may well feel those things) - you're there until the heat death of the universe. An entire page can be written on this, truthfully.
Intangibility - You are immune to gravity or gain some kind of buoyancy, hence not plummeting through the ground. You also gain some self locomotion, so as not to worry about friction, (though many intangibles can float or explicitly fly). You can still interact with air normally allowing you to breathe (if you need to breathe), hear and speak. Furthermore, an Intangible Man is still anchored relative to the Earth. Remembering that Earth whizzes around the Sun at a frankly irresponsible speed, anyone who can walk-through-anything should find themselves suspended in space a few seconds after their powers manifest, watching the Earth slowly but surely arcing away from them...
Nigh Invulnerable - Other than folks who fall under the Made Of Air version of this trope, these characters also frequently exhibit the ability to anchor themselves. Even if they don't take damage from a heavy blow, it should still send them flying if they can't diffuse that much force. This one is more frequently subverted, with characters who resist damage but get knocked around quite easily, which makes for good No One Could Survive That moments. If they have superstrength, they could conceivably be bracing themselves for the blow, but those invulnerable characters without super-strength have no such excuse; this only works up to a point, however, as no amount of strength can defy the laws of motion. Strike someone with enough force, and they will move. (Superman and others of his ilk get a pass again because they can hold themselves in place with their flying powers.) Also, see the page opener quote for more downsides. Again, may be excused if the invulnerability in question is essentially due to Inertial Dampening.
Shooting Ice or Fire
Cryokinesis / Pyrokinesis - Manipulators of heat energy are kicking the laws of thermodynamics in the nads. Either they are explicitly creating/destroying energy (that's the Law of Conservation) or - in the case of those channelling the energy around - they're violating the Second Law of Thermodynamics by 'decreasing entropy.' This sort of violation might not be a full-fledged secondary power, but it's worth thinking about for Harder or Deconstructive works. Secondly, being immune to their own powers is quite important to prevent self-inflicted frostbite or burns. If the power is described as the ability to create and destroy heat energy, instead of explicitly heat or cold, it implies the character should be able to pull double-duty as both a cryokinetic and pyrokinetic. By the same token, psychic powers may theoretically be turning 'mental energy' into other types of energy. Not that that makes any more sense...
Lightning - Unfortunately, one of the coolest powers is a good deal more difficult than pointing your finger and watching it go. If you want to splice together a pet Pikachu, you need to overcome these hurdles first:
Sonic Powers (No, not that) - It's good not to be deafened by your own sonic scream. Not to mention what stronger vibrations can do to unprotected internal organs, especially the vocal chords and breathing passages that actually produce the sounds and are thus in the closest proximity to them. You also need to somehow focus and direct the brunt of the scream, or else it'll go off in a spherical area and with no care to what it destroys or deafens (imagine being near a jet at takeoff, and you get the idea).
Super Reflexes - Generally implies some level of Super Senses and Super Speed. It's no use being able to react to a bullet if you can't even detect it coming, and even then you need to be able to move out of the way in time. All the more so when dealing with especially fast, explosive or close-range munitions.
Super Senses - Clearly, a lot of potential downsides to this one. The ability to selectively screen your input is an absolute necessity unless you want your hero to be called "Captain Migraine", "The Squinter" or "Curled-Up-In-The-Fetal-Position-On-The-Floor Man," and let's not even go over issues with sensitivity in the nether regions. Likewise, being able to see through things is only good if you can also see the outsides of them when necessary. Heroes with this power also seem to automatically gain the skills needed to properly interpret the new sensory input. In reality people tend to struggle when they suddenly gain a new sense, and it can take years to adjust to it.
Super Speed - These characters are somehow immune to the effects of friction - specifically, the chafing that would naturally occur from using extremely rapid speed for extended periods of time, especially while wearing spandex. Again, this is only for characters that aren't explicitly described as Nigh Invulnerable; presumably, that would also cover friction damage. The same applies to the materials in contact with speedster, especially clothes (that should be bent to move): either invulnerability is extended to them or they are going to be damaged and possibly disintegrated/incinerated. For instance, the various speedsters of the The DCU related to The Flash each have a thin invisible aura that protects their bodies from air friction (and, presumably, the impact of their feet hitting the ground at several hundred miles per hour several hundred times per second). This aura also allows them to survive the rigors of outer space. And they face a problem the other direction, of having too little friction. There's a limit to how much lateral force a foot pushing back against a flat surface can create, determined by the coefficient of static friction between the sole of the foot and the ground surface. For typical shoe soles on, say, asphalt or concrete, this coefficient is between 0.8 and 1.0, which means a runner can't produce a forward force greater than 0.8-1.0 times his own weight without his foot slipping. The drag force from plowing through air at super-speed can be colossal, and if the forward force is less than this drag the speedster will slow down. The speed at which an object's drag force equals its own weight is a well-known quantity encountered by skydivers all the time: it's called the terminal velocity. The terminal velocity for a randomly-oriented human body is about 120 miles per hour; for a streamlined head-first human body it's closer to 150 miles per hour. If the speedster wants to run any faster than this, he either needs foot soles with coefficients of friction higher than 1.0, or a means of generating "downforce" to press him onto the pavement harder than his own weight. Feet coming down at superspeed would presumably have super impact, and push them off the ground and at least a few feet in the air. Even once that's explained, someone going at superspeed over the slightest hill, or up stairs, or just random dips in the ground, would lose contact with the ground, they would keep going in the 'same direction' as before, into the air. note The faster ones would be launched into orbit, especially while doing the 'run around the world' trick. They have to have something that holds them in contact with the ground better than gravity if they don't want to end up hurtling comically though the air every other step like a Wuxia character. Speedsters also must possess a very powerful and efficient metabolism, which keeps them from needing to drink several times their weight in pure nectar every day (In recent years, this element has been often used to justify faster healing). Sometimes, this is partly averted - more than one character like this has been shown to be a Big Eater to power their abilities - though not even spending 24/7 in front of an all-you-can-eat ice cream and candy buffet could provide enough calories to power more than a second or two of supersonic running speeds. Which means that every Speedster really is a PerpetuumMobile. Also, they have to have a very high stamina, as running from New York to Los Angeles all at once should be impossible no matter how fast they do it. They also have to have super friction powers (again with the friction), so that they can actually keep their footing when turning on surfaces that aren't specially constructed for high-speed travel. Cars turn easily at sixty miles per hour on (properly angled) asphalt, but they'd have a much harder time at 600 miles per hour on tile. And if their speed is too high for a given viscosity, there's no time for collisions to be resolved quietly, so normally soft substances (like water or plastics) are going to behave like hard ones: literal blades of grass, glass puddles, buckshot raindrops, shrapnel snow, fragile clothes, that sort of thing. Speedsters who pick up or put down anything while speeding also have to have some power that cushions the impact. Otherwise, attempting to grab a person when you're running at a hundred miles an hour wouldn't pick them up, it would snap them in half. If these characters approach the speed of light, they would experience Time Dilation. Furthermore, speedsters never get specks of dust caught in their eyes... They would also need some type of super-concentration. Given that they must have some form of Super Reflexes so they can react normally to things at super-speed, they should perceive normal speed to be horrifyingly slow. Imagine trying to hold a conversation with people who take several hours to speak a single word. Similarly, if a speedster does something like typing millions of password combinations into a computer, he must somehow avoid getting bored after the first few hundred. It is also possible that the refresh rate of a monitor (normally 60 times per second) would be too slow for themnote , or for extreme examples, even the response time of the processor to something like a keyboard interrupt. Alternatively, they may have nervous systems that can multitask at different speeds, allowing them to perform (for example) simple manual tasks at superspeed while only being consciously aware of a few seconds passing. Characters with super speed must also be able to withstand massive G-forces caused by rapid acceleration/deceleration, since most of them are shown to be able to start/stop instantly (rarely applies to those who lack this talent, but they may end up going Too Fast to Stop as a result and find that Inertia Is a Harsh Mistress). This must make the character somehow able to anchor to the ground while stopping too, since friction with the ground can only go so far - but often they just instantly stop. More than likely this uses some form of Inertial Dampening rather than actual friction, as it normally fails to tear up the roadway or set it on fire. Protection for your internal organs from the effects of inertia is also a must, otherwise they'll just liquify and ooze out of your pores at extremely high speeds or fly out of your body when stopping on a dime. Normal humans moving at very high speeds without a protective barrier would forcibly ram-scoop air into their lungs. It'd be like driving without a windshield... on a supersonic jet. So their "aura" must either slow the air, or redirect it safely around them (while still allowing in enough to breathe). There was a real life incident where the navigator in a US Navy KA-6 Tanker ended up hanging out the cockpit of the aircraft. His seat had become detached from the floor due to metal fatigue and ended up pretty much floating on the ejection guide rails. His helmet and oxygen mask were taken off by the wind. Through his apparently being one of the luckiest guys in the world, he survived, and later compared trying to breathe during the ordeal to trying to drink from a firehose. This on a subsonic aircraft with the pilot deliberately flying as slowly as he could (unlike most vehicles, aircraft stall when they fly below a certain speed due to the lack of lift). Also traveling at very high speed would generate shock waves that even if they won't affect the speedster would affect everyone around. And in the cases of extremely high speed, there is also the risk of the radiation (principally Gamma Rays) produced by the Doppler Effect of traveling a such high speeds.
Super Strength - Many characters with super-strength also have super anchoring abilities. This keeps them from being shoved into the ground when they lift up something remarkably heavy, like buildings or land masses. An ability to fly such as Superman's - the ability to support and move your own body in empty space as you wish - could do the trick, as you wouldn't need the ground to support you. A common subversion is a hero that lacks this anchoring ability, thereby heavily restricting what they can lift without sending themselves up to their waist in the ground. Also, characters that are super-strong but not explicitly Nigh Invulnerable have some level of enhanced resistance in their bones. If their super-powerful muscles were anchored by normal bones, the bones would repeatedly be broken apart by the muscles' exertion (or just constantly pulled off the anchor points, resulting in rather horrific sprains). This is not to even say anything about things like punching through stone. To use super strength effectively also requires the ability to strengthen objects by touching them (unless the object is made of some advanced material, of course). Otherwise, holding up (for example) an airplane with one hand would simply result in a hand-shaped hole in the still-plummeting airplane.
Time and Space
Time Freezing - Those that stop time should be blinded. If time were stopped, everything else stops too, including light. And air, which would hold them in place because the air they displace when they move can't get out of the way. In fact, those that stop time should be frozen along with everything else by the mere nature of the ability. One explanation for this is a Time Bubble, where the character stays in bubble of sped up time, thus avoiding many of the problems that speedsters would face (and the bubble must move with you or you're stuck in one spot). Of course, while this solves some of the problems, it merely displaces others. For example, you'd still be blind unless you had a light source in the bubble with you. If you did have a light source, you could see fine inside the bubble, but any photons which hit the edge of the bubble would get "stuck," so you couldn't see anything outside. And when you stopped using your power, all of those "stuck" photons would start moving again at once, resulting in a blinding flash. note . Another scenario is that rather than truly stopping time, the character simply moves really fast so everything else appears to be slower or stopped, like in the movie Clockstoppers, or one Choose Your Own Adventure story where you acquire a device to speed yourself up. Since this still leaves the problem of not being in sync with one's surroundings, for the purposes of this trope it can either be treated the same way as time "stopping", or as super-speed with all its attendant problems. Of course, there are problems with this too: the friction would probably be so great that you, and everything you touch, would either get a large hole in it or catch fire. Over-application of this power should logically lead the user to be significantly older than they should be. This may or may not be addressed, although it really should if several in-story years go by with the character continuing to use it.
Teleportation - Teleportation-users would need to have some way of extending their teleportation to their clothes and items if they do not wish to reach their destination naked. Clothes are one thing but dental fillings, bone pins, pacemakers, etc would be unpleasant to suddenly be without. Ignoring the ludicrousness of trying to extend quantum-scale barrier tunneling to the classical scale (assuming that's how matter teleportation works in your particular 'Verse, or that the Real Life rules of quantum physics even apply at all), such motion usually needs large amounts of energy as well. Long-distance teleporters would also need to compensate for the curvature of the Earth and relative motion of different points on the Earth's surface; someone teleporting from Europe to China would otherwise arrive traveling very, very fast while upside-down. Furthermore they need to be really accurate to avoid falling hundreds of feet on arrival or appearing inside the Earth itself, or something else - and even if they manage to appear in relatively empty space, they need to somehow ensure (1) that the air at the destination does not end up inside their body, causing decompression sickness and a potentially fatal air embolism, and (2) that some matter replaces them at the departure location, to avoid an implosion which would damage things in the area. Best variants so far boil down to cutting an area out of reality and pasting it in at the destination in a speed-synchronized way (of course, the destination area must be instantaneously exchanged with the source). Or a Wormhole, which is basically a spatial shortcut— the real-world physics term for such a hypothetical form of transport is "topological displacement".
Time Travel - Most time-traveling heroes have the benefit of being immune to Temporal Paradox and the physical effects of The Time Traveller's Dilemma. Even if they do accidentally erase their own parents from history or create an even worse Crapsack World by killing Hitler only to have someone worse take over, the hero will remain unchanged and still be capable of trying to Set Right What Once Went Wrong. There's also the problem of traveling only through time and ending up floating in space because surprise, surprise, planets, star systems, and even galaxies happen to move around. Most time travel stories will completely ignore this problem, so the auto-compensation is a Required Secondary Power. Some time machines even teleport to a different place on Earth relative to their starting point, which just happens to be the perfect spot to set the plot rolling, with no specific input from the travelers to go there. The short version is that, if you kept inertia, you would move through space- but you'd wind up nowhere near your planet anyway. The long version is that the time traveler would, unless the time control device had some sort of "Non-relativistic inertial dampener" built in (which would arguably be worse) or had the prerequisite auto-corrector, maintain their current heading and velocity through space at the time they leaped. Unfortunately, this would not take into account changes to the planet's velocity (as often happens, altered subtly by potential events like the gravity of other celestial bodies, meteors or very large explosions) between departure and arrival. However, this is further complicated by one main factor- your velocity being more or less perpendicular to the planet's actual travel path due to planetary spin. Your chances are... bad if you try to jump to the future. You're definitely not making it if you attempt to travel backwards through time under these conditions. Adjusting for changing terrain between leaving and arrival would also be required. Note that these are only problems if the traveler jumps immediately from the departure time to the arrival time without existing in the time in between. If instead, the traveler could change the way time affects him, (such as speeding up time to go to the future or reversing time to go the past), any forces that would affect the rotation of the planet would affect him as well. However, this also has many of the same problems as Time Freezing. There is also the issue of traveling too long. If you're gone for six years, you can't come home on the day you left and expect that nobody notices that you're six years older. Time travelers would need to be immune to the effects of diseases from different time periods. An modern man or woman's immune system would not likely be suited to fighting plagues from 2000 years into the past or future. Similarly, a time traveler risks becoming a Walking Wasteland by bringing germs from his or her own time period to others. If traveling to the past, a person should also be concerned with eating meals that haven't gone through a modern sanitation process. Time travelers also need some sort of resistance to the effects of jet-lag (though this is more prominent in time/space travel). Jumping between times and timezones (for example, from 12 in the afternoon to 12 midnight) would provide similar effects as traveling from Bangalore to San Francisco. Hardly any time travelers have a visible reaction to this, even if their time-travel isn't through the use of powers, but through machinery. Not so much a "required" secondary power, per se, but still notable nonetheless. If a time traveler wants to have any sort of social interaction with the people from the time period, they'll need to do more than just pack period-appropriate attire. Sure, you might know how to dress to blend in to 1940s Germany or Walk Like an Egyptian, but can you speak the language? Understand local customs? Do you have currency that you can spend in that time period/locale? Are you familiar with virtually-universal skills of the period, such as horse riding? For more recent eras, you'd need some form of official ID to function in society. If you want to blend in, you'd need a professor-level knowledge of the time period.... boy, sure starting to feel Made of Plasticine now, aren't you?