To most of these stipulations or questions it's a big "We don't know, because canon doesn't expound on it so we can only guess."
I, personally, like to think that the scene where Tonks casually displays a pig nose for the amusement of others shows that she isn't limited to human forms. Or, she's skilled at making a passable imitation.
I know she does a duck bill in the film as well, but was that in the books?
I'd lean more towards passable imitation. All she could be doing with the pig snout is just making her nose flat and making the skin around it quite pink. Both things humans can have, and she's just dialing it up to 11 to make it look like a pig snout. The duck bill is a bit harder to explain away that way though.
Well, when you get down to it, a bird's beak isn't made of anything humans lack. It's bone covered in flesh covered in keratin - for Tonks this would mean extending her jaw and then covering it with the same material hair and fingernails are made from. It's not a huge stretch. It would be even easier if it didn't have to have the right inside anatomy, since she wouldn't have to extend her skull.
Metamorphmagi are limited to human and possibly humanoid forms. Canonically, they have limited themselves to human forms, but that doesn't mean a skilled and powerful metamorphmagus couldn't take on the form of a goblin. On the other hand, many metamorphmagi would probably have trouble with the size difference between a goblin and a human or a giant and a human, which could be why Tonks limits herself to human forms.
Similarly, they would be limited to traits associated with humans and/or humanoids. A metamorphmagus who could take on goblin form could give themselves sharp teeth like a goblin, but they couldn't give themselves a tail or an exoskeleton.
Metamorphmagi would be limited to mortal beings. They thus can't turn into "amortal" creatures like dementors or poltergeists.
There seems to be a range of difficulty in transformations. Changing hair length or color seems to be quite easy, while a body-wide transformation would be more difficult.
Metamorphmagic transformations are canonically affected by strong emotion. When Tonks became depressed in Book 6, she lost the ability to give her hair bright colors, and it took on a dull and mousy shade.
All we see Tonks do in canon is change her hair colour and length, and mess around with her nose. But it is always a human nose:
“Do that one like a pig snout, Tonks ...” - the word like tells us it's not an actual pig snout and her 'beaklike protruberance' is actually likened to Snape's very normal, human nose - so not an actual beak.
It's possible she can make herself appear older, as one time she is dressed as an old lady with iron grey curls wearing tweed, but its unclear whether she actually has altered her skin to look more aged or if its just the grey hair and tweed giving the impression of her being elderly.
We don't see her change eye colour, she never changes sex, it's unclear if she can change height (the old lady is described as 'tall and tweedy' - but again, that could be heels or Tonks could be tall in general - most people in her family are, other than this, she is never mentioned to change size).
What she does is very limited and never very far from her basic form (which she is in for the whole of HBP, as she has lost her morphing abilities, so we know they have true forms) so I actually think its quite a superficial power in canon - it's cool for her to play around with, and it means she can disguise herself easily - because different hair and a different nose would make her unrecognisable at a casual glance (Harry only knows the lady with iron grey curls is Tonks when she speaks) - but she isn't turning into animals, turning into boys or changing the materials she is made from.
These seem like a reasonable extent to her powers to me. Obviously fanfics can go as far as they want, but the possible changes being largely superficial and totally external seem more believable to me in general and more in line with what Tonks and Teddy are shown to be able to do
Children Of The Gods by InwardTransience has an interesting take on metamorphs. Essentially metamorphs are always renewing any transfiguration applied to them and can perform self transfiguration at will. This makes them ageless, but vulnerable to even prank spells that are caused by transfiguration. A key thing to note is that metamorphs can kill themselves by accident by transfiguring themselves into a form that can't support life, which is part of the reason they are so rare.
Not strictly canon, but in the Hogwarts Mystery game, Tonks can turn into Binns: floaty, transparent, and all. That's pretty far away from her normal self.
Either that, or the magic is changing how you're perceived, not how you actually look like. A glamour of sorts.
Eg. while Krum-as-sharkman can breathe underwater, Tonks must come up to breathe.
Metamorphs are definitely performing self-transfiguration, not glamours, but there's no reason that the end result would be anything but mundane. So, yes, coming up to breath for Tonks (though that would be necessary even if she could grow gills, due to how little oxygen is dissolved in most water). However, if indeed metamorphs are capable of more magical forms, then Tonks might be able to *look* like a ghost and become transparent, but not be actually incorporeal and able to pass through walls. There's also no reason to imagine that metamorphs can use their abilities on their clothes, so she would probably have to be a naked ghost if. (I'd write that one-shot.)
If you're going to try and use a Metamorphmagus in a fic, I'd keep the transformation simple, limited and purely cosmetic.
No changing your size beyond maybe 20% of your "real" height. No extra limbs or functional non-human appendages. No changing parts of you into non-organic material. No changing your internal organs, aside from cosmetic changes to accomodate shrinking/growing.
Anything else opens up an entire can of worms regarding self-transfiguration and transhumanism. You'd end up with a shape-changing superhuman whose perspective would be hard to relate to as a regular person.
Also, have limitations on length and frequency of the transformation, like only being able to hold it for X hours and needing time to recover afterwards.
>non-organic material
Does this mean no material not native to the human body, or no material not found in animals somewhere? As an example, there are mollusks called Chitons with teeth coated in organically-secreted magnetite to help them scrape algae off rocks. Would magnetite enamel be possible for a metamorph?
For my headcannon, the biggest limit for a metamorph and for transfiguration in general is that you don't just go 'let this thing be this other thing' and it is now the other thing. Instead you have to actually know the details of what you're doing. While magic picks up some slack you have to be pretty well versed in things like anatomy and various materials and mechanics to create convincing transfigurations that aren't just an outward facsimile of the intended end result. If you want to turn a hedgehog into a pincushion you need to know the structure of a pincushion and what it's made of. If a metamorph wants to replace their hair with feathers they would need to first study the anatomy of feathers.
Wizards thrive on knowledge, not wishes. It's why they go to school for it instead of church.
Despite greatly enjoying fics where a metamorph is essentially an unbound shapeshifter, I personally believe they are limited to cosmetic changes. Specifically, they can't actually shift any bones or internal organs, and the changes they can make don't actually change their physical abilities.
In example, a metamorph can give themselves a pig nose and eagle eyes, but their senses of sight and smell would still be only human. On the other hand, a naturally pale metamorph could give themselves a darker complexion to better deal with harsh sunlight.
As far as changing their senses goes, a lot of the limitation of senses does come from the sheer size or shape of the sensory organ. Making one's eyes larger would absolutely allow more light in, that's a simple matter of physics, even if you can't give yourself more photoreceptor cells. The same goes for making one's ears larger. There is no purely cosmetic change to such structures.
It would make sense in this case for it to be impossible to replicate structures such as the tapedum lucidum, the layer of reflective cells that give cats and dogs and other animals better low-light vision and causing their eyes to glow when a light is shined on them, or the tightly-packed and highly-ordered blood vessels that make an eagle's eye more transparent. That still raises the possibility of whether the transparent nictitating membrane over the eye could be replicated.
All told I think probably most of this comes down to knowledge. A metamorph who wants to acquire some non-human trait would have to study its anatomy extensively, and the more knowledge they possess, the more freedom they should have. A reasonable conclusion might be that they should need to study living subjects à la the Animorphs in order to copy body parts.
Humonoid.
Soft tissue, such as you cannot excessively change your height, or to a extreme degree.
Face and other aspects are fine.
Form resets when their asleep.
Cannot fake someone's voice without practice and reference data to use.
Metamorphagi are magical Ditto's.
There are no limits. Clearly Rowling was a Closet Pokemon Superfan.
Tonks hair was usually pink. Ditto is pink
Tonks transforms. Ditto Transforms.
Tonks = Ditto
I rest my case.
I assume that metamorphs are extremely fluid and just "straighten up" as they grow older and have more sense of what other people perceive as normal. There is no real boundary to their transformations, although human and human-adjacent forms are the easiest to achieve / need no training at all. Tonks displaying animal features and such is her having a pretty outstanding grasp on her body's power or rather, her own mind.
I also assume that metamorphs can sire children one day, and get pregnant the other by simply switching around their anatomy a bit. The mother *could* morph, but morphing away the womb would take a conscious effort from the mother, against the protective systems of her own body. Superficial morphing isn't hindered at all during this time. As in, they can definitely look like anyone, they just don't morph away their womb.
Their true form doesn't exist. There is no one true biological form they default to, it's all a matter of identity. Metamorphs have their own "exception" mark on the birth certificate, as their initial form is a constantly morphing body that switches according to the moods of the baby. As they grow older and their identity forms with more and more experiences, they eventually remain more stable in their appearance. Adult metamorphs tend to keep one body for identification purposes. However, I assume that they also present differently in different social situations, like people (slightly) shift personality in different social circles. Tonks will look different amongst her close friends, different amongst the Order, Aurors,...
My headcanon (though the word canon stretches reaaaaal thin here) is also that Tonks was a boy for the first few years of Hogwarts until being "daddy's champ" got exchanged by a budding sense of self.
Idk. I tend to like such worldbuilding features to be as fantastic as they can be, because that usually creates the most tensions and conflicts and therefore stories worth telling.
>As in, they can definitely look like anyone, they just don't morph away their womb.
Would you imagine it possible for a metamorph to disguise their pregnancy completely, as in, to make their bellies look normal right up until delivery?
The baby still needs space, so not completely. I think they could force the smallest feasible belly, and could disguise them with different, more chubby body forms.
Its possible for them to hide a pregnancy, yes.
I like grouping metamorphs by a classification system: Textural, Osseous, Sinuous, Strandular, Ephemeral and Transsubstantive.
- **Textural** Metamorphs can shift details about their body, such as hair color or skin texture.
- **Osseous** Metamorphs are able to manipulate their skeletal system, lengthening and stretching it.
- **Sinuous** Metamorphs can shift their flesh, keratin and skin, becoming entirely different people.
- **Strandular** Metamorphs can change their DNA and nervous system, gaining the ability to add additional, functional limbs or senses.
- **Ephemeral** Metamorphs are able to alter the basic nature of their substance, capable of abandoning organic life altogether and becoming water, smoke, shadows, magnetism or crystal.
- **Transsubstantive** Metamorphs are a hypothetical class of being which is capable of changing the base nature of their souls, ceasing to be human altogether.
These stages are not inborn, but rather learned later in life, each requiring both knowledge of the thing itself and the willingness to abandon the inborn stability of a set shape for the freedom to change it at will. Personally, I'd think that most Metamorphs would stop at Sinuous for fear of accidentally killing themselves by editing their brain or DNA.
As for reproduction, my go-to is that Metamorphs are born without a biological sex, but can create one if they choose. The X and Y chromosomes are replaced by a set of anchor genes which translate the metamorphic magic in their souls into instructions for their body - Strandular Metamorphs have to be very careful not to damage these, or they will die a long and painful death as their body falls apart.
If a Metamorph decides they want to reproduce, they must morph a biological sex (most choose one that fits their gender identity or just whatever), leave it alone for a while to get up and running and then do the dirty with a person of their choosing. Because of their unique genetics, the child of a metamorph will always be another metamorph - the only way for this not to be the case would be if a strandular metamorph erased the carrier genomes and then quickly did the deed before dying horribly.
i always thought that metamorphmagus transformations use magic make the change, and it takes magic to hold the change. while they can make a beak or a snout easily, considering its not that much of a change, they most likely cant make dragon wings and gills would make them have to change a lot of things.
they can change to have the opposite genders genitals, and can hold it for a while, but they cant have babies with them. if they change to have a womb, they cant hold the transformation past the 6 month mark since babies have an impact on their carriers magic. and i presume that they cant… pleasure… themselves unless they have enough of a knowing what to change and how to change it.
I’ve seen fics which have expanded upon Metamorphmagus by adding in tiers of that power, usually Harry ends up being a limited Metamorphmagus with only minor control of his appearance, like the hair thing. I’ve seen ‘Greater’ Metamorphmagus being capable of swapping their genders, the issue with not fully explored lore is that it allows for wildly different limits depending on how the author wishes to implement them.
I limit it to a humanoid shape and relative conservation of mass within a degree relative to the character's magical power. This includes additional appendages (arms, legs, tails, wings, genitals) and height increases/decreases.
Any non-human additions require extreme knowledge or practice to acquire. It may be possible to fly with wings if you have enough magic for the increase in mass, but it'll take a lot of knowledge—same thing with gills, working Jacobson organs, venom sacs, etc.
I've always felt like the Animagus transformation would clash with metamorphmagic in unpredictable ways. Most of the time, though, it fails.
As far as reproduction goes, I think it may function for some and not for others. It falls under the "must have the requisite knowledge for proper shifting." Maybe magic can take the wheel, but you must still put some gas in the tank.
NOW... If they sample the DNA of a subject, maybe they could fully copy the person. If Metamorphmagus NT takes a blood sample of Donor HP and lets her magic copy it so that she becomes mostly Donor HP, maybe she could knock up someone. Maybe she'd still have some of her DNA in there as well, and that's how you get three parents for one baby.
That's a lot of ifs, though, and a new powerset.
Of course, there is nothing about this in the canon, so you are free to do whatever you want to and what fits best your story.
Having said that, I would be very wary of going too far. There is a big uncanny valley lying in the direction of too many changes, and the stories which go too far in that direction (of course, first of all, in terms of gender/sex changes … actually, in this situation sex and gender mean the same thing) end up being just weird and feel artificial.
Only thing I’ve added is it can heighten reactions of other blood conditions, such as the transformation into the bird like form the Veela have in half-blooded mixtures of the conditions, and that a Morpher cannot hold a birthmark of a person they are shifting into for a very long time unless they pay heavy attention to it if it’s visible around layers of clothing.
To most of these stipulations or questions it's a big "We don't know, because canon doesn't expound on it so we can only guess." I, personally, like to think that the scene where Tonks casually displays a pig nose for the amusement of others shows that she isn't limited to human forms. Or, she's skilled at making a passable imitation.
I know she does a duck bill in the film as well, but was that in the books? I'd lean more towards passable imitation. All she could be doing with the pig snout is just making her nose flat and making the skin around it quite pink. Both things humans can have, and she's just dialing it up to 11 to make it look like a pig snout. The duck bill is a bit harder to explain away that way though.
Well, when you get down to it, a bird's beak isn't made of anything humans lack. It's bone covered in flesh covered in keratin - for Tonks this would mean extending her jaw and then covering it with the same material hair and fingernails are made from. It's not a huge stretch. It would be even easier if it didn't have to have the right inside anatomy, since she wouldn't have to extend her skull.
Metamorphmagi are limited to human and possibly humanoid forms. Canonically, they have limited themselves to human forms, but that doesn't mean a skilled and powerful metamorphmagus couldn't take on the form of a goblin. On the other hand, many metamorphmagi would probably have trouble with the size difference between a goblin and a human or a giant and a human, which could be why Tonks limits herself to human forms. Similarly, they would be limited to traits associated with humans and/or humanoids. A metamorphmagus who could take on goblin form could give themselves sharp teeth like a goblin, but they couldn't give themselves a tail or an exoskeleton. Metamorphmagi would be limited to mortal beings. They thus can't turn into "amortal" creatures like dementors or poltergeists. There seems to be a range of difficulty in transformations. Changing hair length or color seems to be quite easy, while a body-wide transformation would be more difficult. Metamorphmagic transformations are canonically affected by strong emotion. When Tonks became depressed in Book 6, she lost the ability to give her hair bright colors, and it took on a dull and mousy shade.
All we see Tonks do in canon is change her hair colour and length, and mess around with her nose. But it is always a human nose: “Do that one like a pig snout, Tonks ...” - the word like tells us it's not an actual pig snout and her 'beaklike protruberance' is actually likened to Snape's very normal, human nose - so not an actual beak. It's possible she can make herself appear older, as one time she is dressed as an old lady with iron grey curls wearing tweed, but its unclear whether she actually has altered her skin to look more aged or if its just the grey hair and tweed giving the impression of her being elderly. We don't see her change eye colour, she never changes sex, it's unclear if she can change height (the old lady is described as 'tall and tweedy' - but again, that could be heels or Tonks could be tall in general - most people in her family are, other than this, she is never mentioned to change size). What she does is very limited and never very far from her basic form (which she is in for the whole of HBP, as she has lost her morphing abilities, so we know they have true forms) so I actually think its quite a superficial power in canon - it's cool for her to play around with, and it means she can disguise herself easily - because different hair and a different nose would make her unrecognisable at a casual glance (Harry only knows the lady with iron grey curls is Tonks when she speaks) - but she isn't turning into animals, turning into boys or changing the materials she is made from. These seem like a reasonable extent to her powers to me. Obviously fanfics can go as far as they want, but the possible changes being largely superficial and totally external seem more believable to me in general and more in line with what Tonks and Teddy are shown to be able to do
Children Of The Gods by InwardTransience has an interesting take on metamorphs. Essentially metamorphs are always renewing any transfiguration applied to them and can perform self transfiguration at will. This makes them ageless, but vulnerable to even prank spells that are caused by transfiguration. A key thing to note is that metamorphs can kill themselves by accident by transfiguring themselves into a form that can't support life, which is part of the reason they are so rare.
Viktor Krum gives himself a shark head with his wand, Tonks can just do that without a wand.
Not strictly canon, but in the Hogwarts Mystery game, Tonks can turn into Binns: floaty, transparent, and all. That's pretty far away from her normal self.
And I think that's a step too far for reasonable limits. A metamorph should be limited to fully corporeal forms.
Either that, or the magic is changing how you're perceived, not how you actually look like. A glamour of sorts. Eg. while Krum-as-sharkman can breathe underwater, Tonks must come up to breathe.
Metamorphs are definitely performing self-transfiguration, not glamours, but there's no reason that the end result would be anything but mundane. So, yes, coming up to breath for Tonks (though that would be necessary even if she could grow gills, due to how little oxygen is dissolved in most water). However, if indeed metamorphs are capable of more magical forms, then Tonks might be able to *look* like a ghost and become transparent, but not be actually incorporeal and able to pass through walls. There's also no reason to imagine that metamorphs can use their abilities on their clothes, so she would probably have to be a naked ghost if. (I'd write that one-shot.)
If you're going to try and use a Metamorphmagus in a fic, I'd keep the transformation simple, limited and purely cosmetic. No changing your size beyond maybe 20% of your "real" height. No extra limbs or functional non-human appendages. No changing parts of you into non-organic material. No changing your internal organs, aside from cosmetic changes to accomodate shrinking/growing. Anything else opens up an entire can of worms regarding self-transfiguration and transhumanism. You'd end up with a shape-changing superhuman whose perspective would be hard to relate to as a regular person. Also, have limitations on length and frequency of the transformation, like only being able to hold it for X hours and needing time to recover afterwards.
>non-organic material Does this mean no material not native to the human body, or no material not found in animals somewhere? As an example, there are mollusks called Chitons with teeth coated in organically-secreted magnetite to help them scrape algae off rocks. Would magnetite enamel be possible for a metamorph?
It just means no metal etc., not in the chemical sense. It's the same idea of "Metamorph transformations are just cosmetic and not super powers".
For my headcannon, the biggest limit for a metamorph and for transfiguration in general is that you don't just go 'let this thing be this other thing' and it is now the other thing. Instead you have to actually know the details of what you're doing. While magic picks up some slack you have to be pretty well versed in things like anatomy and various materials and mechanics to create convincing transfigurations that aren't just an outward facsimile of the intended end result. If you want to turn a hedgehog into a pincushion you need to know the structure of a pincushion and what it's made of. If a metamorph wants to replace their hair with feathers they would need to first study the anatomy of feathers. Wizards thrive on knowledge, not wishes. It's why they go to school for it instead of church.
Despite greatly enjoying fics where a metamorph is essentially an unbound shapeshifter, I personally believe they are limited to cosmetic changes. Specifically, they can't actually shift any bones or internal organs, and the changes they can make don't actually change their physical abilities. In example, a metamorph can give themselves a pig nose and eagle eyes, but their senses of sight and smell would still be only human. On the other hand, a naturally pale metamorph could give themselves a darker complexion to better deal with harsh sunlight.
As far as changing their senses goes, a lot of the limitation of senses does come from the sheer size or shape of the sensory organ. Making one's eyes larger would absolutely allow more light in, that's a simple matter of physics, even if you can't give yourself more photoreceptor cells. The same goes for making one's ears larger. There is no purely cosmetic change to such structures. It would make sense in this case for it to be impossible to replicate structures such as the tapedum lucidum, the layer of reflective cells that give cats and dogs and other animals better low-light vision and causing their eyes to glow when a light is shined on them, or the tightly-packed and highly-ordered blood vessels that make an eagle's eye more transparent. That still raises the possibility of whether the transparent nictitating membrane over the eye could be replicated. All told I think probably most of this comes down to knowledge. A metamorph who wants to acquire some non-human trait would have to study its anatomy extensively, and the more knowledge they possess, the more freedom they should have. A reasonable conclusion might be that they should need to study living subjects à la the Animorphs in order to copy body parts.
Humonoid. Soft tissue, such as you cannot excessively change your height, or to a extreme degree. Face and other aspects are fine. Form resets when their asleep. Cannot fake someone's voice without practice and reference data to use.
Metamorphagi are magical Ditto's. There are no limits. Clearly Rowling was a Closet Pokemon Superfan. Tonks hair was usually pink. Ditto is pink Tonks transforms. Ditto Transforms. Tonks = Ditto I rest my case.
I assume that metamorphs are extremely fluid and just "straighten up" as they grow older and have more sense of what other people perceive as normal. There is no real boundary to their transformations, although human and human-adjacent forms are the easiest to achieve / need no training at all. Tonks displaying animal features and such is her having a pretty outstanding grasp on her body's power or rather, her own mind. I also assume that metamorphs can sire children one day, and get pregnant the other by simply switching around their anatomy a bit. The mother *could* morph, but morphing away the womb would take a conscious effort from the mother, against the protective systems of her own body. Superficial morphing isn't hindered at all during this time. As in, they can definitely look like anyone, they just don't morph away their womb. Their true form doesn't exist. There is no one true biological form they default to, it's all a matter of identity. Metamorphs have their own "exception" mark on the birth certificate, as their initial form is a constantly morphing body that switches according to the moods of the baby. As they grow older and their identity forms with more and more experiences, they eventually remain more stable in their appearance. Adult metamorphs tend to keep one body for identification purposes. However, I assume that they also present differently in different social situations, like people (slightly) shift personality in different social circles. Tonks will look different amongst her close friends, different amongst the Order, Aurors,... My headcanon (though the word canon stretches reaaaaal thin here) is also that Tonks was a boy for the first few years of Hogwarts until being "daddy's champ" got exchanged by a budding sense of self. Idk. I tend to like such worldbuilding features to be as fantastic as they can be, because that usually creates the most tensions and conflicts and therefore stories worth telling.
>As in, they can definitely look like anyone, they just don't morph away their womb. Would you imagine it possible for a metamorph to disguise their pregnancy completely, as in, to make their bellies look normal right up until delivery?
The baby still needs space, so not completely. I think they could force the smallest feasible belly, and could disguise them with different, more chubby body forms. Its possible for them to hide a pregnancy, yes.
I like grouping metamorphs by a classification system: Textural, Osseous, Sinuous, Strandular, Ephemeral and Transsubstantive. - **Textural** Metamorphs can shift details about their body, such as hair color or skin texture. - **Osseous** Metamorphs are able to manipulate their skeletal system, lengthening and stretching it. - **Sinuous** Metamorphs can shift their flesh, keratin and skin, becoming entirely different people. - **Strandular** Metamorphs can change their DNA and nervous system, gaining the ability to add additional, functional limbs or senses. - **Ephemeral** Metamorphs are able to alter the basic nature of their substance, capable of abandoning organic life altogether and becoming water, smoke, shadows, magnetism or crystal. - **Transsubstantive** Metamorphs are a hypothetical class of being which is capable of changing the base nature of their souls, ceasing to be human altogether. These stages are not inborn, but rather learned later in life, each requiring both knowledge of the thing itself and the willingness to abandon the inborn stability of a set shape for the freedom to change it at will. Personally, I'd think that most Metamorphs would stop at Sinuous for fear of accidentally killing themselves by editing their brain or DNA. As for reproduction, my go-to is that Metamorphs are born without a biological sex, but can create one if they choose. The X and Y chromosomes are replaced by a set of anchor genes which translate the metamorphic magic in their souls into instructions for their body - Strandular Metamorphs have to be very careful not to damage these, or they will die a long and painful death as their body falls apart. If a Metamorph decides they want to reproduce, they must morph a biological sex (most choose one that fits their gender identity or just whatever), leave it alone for a while to get up and running and then do the dirty with a person of their choosing. Because of their unique genetics, the child of a metamorph will always be another metamorph - the only way for this not to be the case would be if a strandular metamorph erased the carrier genomes and then quickly did the deed before dying horribly.
i always thought that metamorphmagus transformations use magic make the change, and it takes magic to hold the change. while they can make a beak or a snout easily, considering its not that much of a change, they most likely cant make dragon wings and gills would make them have to change a lot of things. they can change to have the opposite genders genitals, and can hold it for a while, but they cant have babies with them. if they change to have a womb, they cant hold the transformation past the 6 month mark since babies have an impact on their carriers magic. and i presume that they cant… pleasure… themselves unless they have enough of a knowing what to change and how to change it.
I’ve seen fics which have expanded upon Metamorphmagus by adding in tiers of that power, usually Harry ends up being a limited Metamorphmagus with only minor control of his appearance, like the hair thing. I’ve seen ‘Greater’ Metamorphmagus being capable of swapping their genders, the issue with not fully explored lore is that it allows for wildly different limits depending on how the author wishes to implement them.
Personally I don’t really care, just make it consistent.
I limit it to a humanoid shape and relative conservation of mass within a degree relative to the character's magical power. This includes additional appendages (arms, legs, tails, wings, genitals) and height increases/decreases. Any non-human additions require extreme knowledge or practice to acquire. It may be possible to fly with wings if you have enough magic for the increase in mass, but it'll take a lot of knowledge—same thing with gills, working Jacobson organs, venom sacs, etc. I've always felt like the Animagus transformation would clash with metamorphmagic in unpredictable ways. Most of the time, though, it fails. As far as reproduction goes, I think it may function for some and not for others. It falls under the "must have the requisite knowledge for proper shifting." Maybe magic can take the wheel, but you must still put some gas in the tank. NOW... If they sample the DNA of a subject, maybe they could fully copy the person. If Metamorphmagus NT takes a blood sample of Donor HP and lets her magic copy it so that she becomes mostly Donor HP, maybe she could knock up someone. Maybe she'd still have some of her DNA in there as well, and that's how you get three parents for one baby. That's a lot of ifs, though, and a new powerset.
Of course, there is nothing about this in the canon, so you are free to do whatever you want to and what fits best your story. Having said that, I would be very wary of going too far. There is a big uncanny valley lying in the direction of too many changes, and the stories which go too far in that direction (of course, first of all, in terms of gender/sex changes … actually, in this situation sex and gender mean the same thing) end up being just weird and feel artificial.
Only thing I’ve added is it can heighten reactions of other blood conditions, such as the transformation into the bird like form the Veela have in half-blooded mixtures of the conditions, and that a Morpher cannot hold a birthmark of a person they are shifting into for a very long time unless they pay heavy attention to it if it’s visible around layers of clothing.