I have a shapeshifter character whose power-set is relatively grounded. They can only change into other human forms. They can basically impersonate anyone they want, so they use their powers primarily for spying purposes. But I’m struggling to imagine how exactly they’d be able to change their height/size. And I’m also unsure as to what limitations there should be. Should they be able to grow beyond 50 feet tall or should there be a limit? Should they be able to impersonate people of different genders? If so, how would they shift around their sexual organs? Should they be able to impersonate people of different ages? Even a newborn? I know that shapeshifting is fictional, but surely there are ways to make it plausible in theory. I am aware that variations of this question have already been asked on here, but I didn’t fully understand a lot of the answers given, as they were very technical.

  • $\begingroup$ It is important to note that molecules can’t be destroyed or created. So the shapeshifter will have to use the molecules of their body to change. They may not be able to become a baby but they can change their age appearance. $\endgroup$
    – Martamo
    May 25, 2023 at 19:47
  • $\begingroup$ Too many questions. This is too open ended. Since the closest we've got to a shape shifter is chameleonic color changing, it's pretty difficult to answer this "science based." $\endgroup$
    – Boba Fit
    May 25, 2023 at 20:27
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    $\begingroup$ If they're not undergoing mass-change (thus limiting them to shapeshifting to those similar in size/volume), then we need something radically different underneath their skin. Instead of smooth muscle for each hair follicle, we'll have a layer of (probably) striated muscle thick enough to flex and expand features. In the face and to a lesser extent upper body. Chromatophores to change skin ton, etc. Perhaps even an unfused skull. $\endgroup$
    – John O
    May 25, 2023 at 21:53
  • $\begingroup$ Is it a biological creature or artificially made? $\endgroup$ May 26, 2023 at 9:47
  • $\begingroup$ @KrišjānisLiepiņš It’s a human being who fell into some plasm that makes their skin and bones malleable like clay $\endgroup$ May 26, 2023 at 14:13

3 Answers 3


You can't change their mass, unless they can quickly absorb or eliminate water.

I'd treat the shapeshifter much like an Octopus; which has no skeleton. The only hard part is the beak; much like a bird's beak. But no skull, the body has an outer layer of muscle.

So it can change color, contort itself into crazy shapes, etc. Maybe it could even simulate hair, if the control is fine enough, or maybe it can extrude hair and re-absorb it.

It could appear to be fat, but it would just be inflating itself.

The same thing for genitals, and breasts. It would be able to simulate either male or female (or it could be "smooth around the bend").

I would guess it cannot be a baby, maybe the size of a 12 year old, and no reason it couldn't be 7 feet tall, fat or thin or (in appearance) muscular.

Octopi have incredible ability for mimicry in their appearance, they can literally make themselves virtually invisible by making their body look like the background; even a rough and non-uniform background. They can make themselves look like sand, like rocks, like plants, like a rough surface, like smooth one. Colors and texture can both be copied.

I don't think it is a stretch for your shapeshifter to look exactly like somebody they want to look like, and if they have the fingerprints, to copy them also.

They may also be able to look like a trashcan, or a section of a brick wall. Perhaps some medium sized item in a store or office, like a desk.

I think your size limitations are a good idea. They cannot impersonate an aircraft, for example. And I would not give them any powers like flight, or impersonating a working machine like a car or a blender or even a bicycle. Just the appearances of them. But they might impersonate a living lion or panther, or a gorilla. Not an elephant or blue whale, not a sparrow, but animals reasonably within the weight range of say 80 pounds to 500 pounds (remembering the shapeshifter would just be hollow when impersonating something large).

I'd go with the ability to extrude and reabsorb "hair". It may be a stretch, but I don't think it is a deal breaker at all.

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    $\begingroup$ I personally disagree with them being able to impersonate non-human objects. Though they could lean against a wall and flatten themselves (and thus blend in somewhat, from a distant observer in a dark alley), they wouldn't be able to shape themselves like a desk, at least not one that'd pass a precursory glance. They'd have a vaguely human shape (head, 2 arm tentacles, 2 leg tentacles), and different parts can change size but they couldn't disguise themselves as anything except a human. Though, if they need to they could disguise as a large dog, at least on a dark night from a distance. $\endgroup$
    – Katy
    May 26, 2023 at 6:44
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    $\begingroup$ @Katy have you looked at any video footage of an octopus camoflaging itself? there are times when you can watch the octopus making the transition and still not be able to obviously see that it is an octopus afterwards. The trick is remarkably effective. $\endgroup$ May 26, 2023 at 9:20
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    $\begingroup$ @StarfishPrime Exactly so. In the lab they can look like a checkerboard, or patterned wallpaper. Moving along the sea floor they can look damn near transparent, and seemingly disappear when they stop. They can look like undersea plants. It is the closest real-life thing on Earth to a cloak of invisibility. $\endgroup$
    – Amadeus
    May 26, 2023 at 9:57
  • $\begingroup$ @StarfishPrime the limited amount I've seen is pretty good, but I thought that in many human environments it may not look passable- a brick pattern would look off on a 3D creature. Though, Amadeus says otherwise- octopi blending in with checkerboards is pretty close to somebody blending in on a brick wall! However, I stand by the shapeshifter being unable to appear like a desk or such. They'd be limited in exactly what shape they can have just by biology, and I'd say "resolution" (AKA, how detailed their disguised skin looks) would also be a limiting factor. So, no IRL gMod prophunt. $\endgroup$
    – Katy
    May 26, 2023 at 12:05
  • $\begingroup$ @Katy a comparison might be drawn to modern soldiers and urban camoflage techniques. Neither the soldiers nor the camoflage patterns are necessarily square, but the ability to break up outlines and look less like a person remains surprisingly effective. Biomimicry of brick patterns may not withstand close inspection, but most people aren't closely inspecting mortar spacing and coloration. If you don't, you may allow the changer to escape or ambush you. If you do, you may waste time and they can escape you whilst you're prodding each floor tile in turn with a stick in a huge open office, etc. $\endgroup$ May 26, 2023 at 12:53

I said this in a comment but have decided to actually answer. There is the law known as the Conservation of Matter. If you want a realistic shapeshifter then they need to rule this law. When shapeshifting they cannot add or remove atoms from their body. So, they cannot become the size of a baby unless they want to die(That is my idea, they will probably just die from losing a lot of body mass). If all you want your character to do is change their appearance then you don't need to do anything. For a shapeshifter to change into another form, like a bull, then they would be a smaller bull. If it is a dog, then a bigger dog(though dogs can get massive).

  • $\begingroup$ becoming bigger might not be that much of a problem, up to a certain pont. The shapeshifter could form pockets of air inside its body to compensate for the missing volume. So it could become the size of "the mountain" from GoT but still be only the weight of a normal person, or whatever its weight is $\endgroup$
    – datacube
    May 26, 2023 at 7:03
  • $\begingroup$ @datacube They could make themselves bouncy and float around. $\endgroup$
    – Martamo
    May 27, 2023 at 13:50
  • $\begingroup$ floating: no, since the pockets would be filled with air, they could never get lighter than air. But depending on the constraints the author sets on a "minimum thickness" he could get really big and therefore have a really high air resistance. bouncy would be for the author to decide, but i'd tend to: "a bit" $\endgroup$
    – datacube
    May 30, 2023 at 4:43
  • $\begingroup$ You're right. It would need to be a lighter than air gas to allow the shapeshifter to float. $\endgroup$
    – Martamo
    May 30, 2023 at 4:59

The other answers by @Amadeus and @Martamo have detailed how through conservation of matter, the shapeshifter wouldn't be able to grow super large or super small, nor would they be able to change their age, only changing how they appear. Therefore, I won't go into detail about similar topics. However, part of your question is how a person could shapeshift and to what extent they could, for instance whether they could change their sex organs or not.

If shapeshifters were possible in real life, they would probably implement the use of stem cells. If a person or other organism could change all their cells into stem cells, rearrange them, and then convert the stem cells back to regular cells, then the person would be able to change face details to look like someone else, including color of eyes and hair, as well as changing their reproductive organs. The person would still be working within the limitations of their number of cells, and of course it is impossible in reality for humans to convert all their cells to stem cells at will, but stem cells would be an important part of shapeshifting in a hypothetical situation.

So while a shapeshifter wouldn't be able to grow 50 feet tall or change into a newborn, they could implement stem cells to change organs and features.

  • $\begingroup$ Wouldn’t this take a while though? It takes nine months for the stem cells of a human embryo to make a little person. If they want to change their eye color, wouldn’t they also need to change their DNA? Because most facial and bodily features are determined by the DNA. $\endgroup$
    – Martamo
    May 30, 2023 at 23:17
  • $\begingroup$ @Martamo you make a fair point. However, assuming shapeshifting is biologically possible, which is isn't, stem cells make the most sense for how it could be done. Yes, in reality it takes a while for stem cells to form new structures, but if it could be done instantaneously and a person could have control over what they shapeshifting into, it would be the best scientific explanation. As for DNA, I think that shapeshifting in general would require changing or overriding DNA. After all, your changing what you look like in many capacities. If you can't control DNA, you can't change shape at all. $\endgroup$ May 30, 2023 at 23:54

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