Heya. Clearly, I am too lazy to go searching through fictions on the site to answer my questions, so I approach you lot instead. (Don't feel like second rates. I highly value all of your opinions. Sometimes.) Anyways, I have noticed for a while now that there is a small trend of fics starring non-human (let me just say NH because my fingers are tired and I'm sure your eyes are too) main characters revolving around this website. And no, I don't just mean 'humanoid' monsters like a certain demon girl, but also stuff like... slimes. Or potatoes. Creatures that are completely different from humans. 

So here are my questions for you to answer.
- Does it ruin the story completely if that creature is able to transform into a human?
*In case you don't know, the reason why some authors do this cough, me, is not just because I like my characters to have limbs and abs, but because it is a lot easier to simply write out the story if the character is human. I mean stuff like facial features, movements, actions and even sometimes fight scenes. Would it be acceptable if it was well-done (meaning the character doesn't become just a normal human) and didn't completely draw away from the premise of this supernatural, unhuman-like creature?*

Wait I lied, that was my only question and now I can't think of anything else to say. Well this is awkward...

Well, I too happen to be writing a NH protagonist. He's a goat... yep. It's an Isekai story revolving around the adventures of a goat in a dark fantasy setting.😅

As you stated, it's becoming more common to see MCs that aren't completely human or not human at all. I recently read a story where the MC is a fish. It was fun but it also came with problems.

Like, a fish can't really express itself beyond just talking (which this fish could do) and this led to the protagonist feeling stiff.

As for me, I ended up having to turn my protagonist into a half man/goat hybrid to allow him to express more emotion and whatnot. I speak only for myself, but I don't think this ruined the story since he still retained many goat-like features.

But this may not work in stories where the plot relies on the fact that the protagonist is NH.

Crap! I went on a tangent and forgot to answer upu question:

No. As long as the protagonist is fun, I don't think it matters what form that take as long as it makes sense in the world their in.👍

From what I've seen, most of the audience will be fine with it, and are used to every monster MC quickly (sometimes, VERY quickly) evolving into a humanoid form, but from there the stories often take a major turn and never feel the same again. A minority will hate that, scream "not again!!!" in agony and roll their eyes, maybe leave a spicy comment or two.

I'm doing a monster MC story too, and it looks like a 80-20 split roughly. If I ever do a humanoid-form-evolution chapter (and I think I never will), I would expect a portion of people to just leave for good

Well it works for That Time I Got Reincarnated as a Slime, which is a very popular manga/anime wherein the main character is a slime who can in fact transform into a human form in order to better interact with other characters.

You're overthinking it, really.

Yes, some people will probably not like the story if your character can transform. That's fine. That means they aren't your audience. You can't please everyone and it's madness to try. Write the story you want to write, with the knowledge that the more niche the character the more polarized opinions of them will be.

I personally find it cheap, I mean at that point just write a human protagonist that occasionally transforms into a monster(s).

I really dislike the trope of turning into a human to make things easier. I want to see a slime struggle to open a bloody door with the key already inside. Transforming into a human just takes away all the charm the story could have had for me.
Which is why I don't do that, but I gave the dragons thumbs, so they are not useless.

Oh, to actually answer the question about my reading preferences, for me it would mostly ruin the story, yes. The only one I read until end like that was Everybody Loves Large Chests, but he was still pretty Mimic-like even when he transformed into humanoids, he still retained most of his old personality. (I didn't like the whole arc of being a catgirl with the young elf gf, that part of the story was pretty annoying to me.)

Good question, I have a non-human protagonist that starts its journey as a rat in a dungeon, but it soon states that its goal is to change back into a human, so in my case I doubt it will ruin the story as it progresively gets a more humanoid form.

I would consider it is well done as long as the character keeps its unique features, I think. Like, don't make him a generic human being with good looks or something. Another point would be how the change fits in the history and also the role of the human form, is it just going to stay a human all the time from now on? Is there any limitations to it? Does the MC have a need to revert to his non humanoid form?

PD: I also feel the pain of writing fighting scenes, my rat is only good a biting, not a lot of variation in there, I kinda went around it making it approach some combats with a strategy in mind.

There are a couple of different ways nonhuman MCs can go.

If you have a nonhuman MC in a human-shaped world then being nonhuman gets boring pretty fast and if the option to change shape is available it makes sense to use it. It would be like insisting that your screwdriver is just as good a hammer as a hammer and refusing to nail the nail with a hammer because you have a screwdriver, at a certain point it loses its quirky nature and is just frustrating. Just use the hammer, just use the human shape. This doesn't have to be a "cheat" or a copout if your MC considers this to be "just another tool" and has other shapes they use for other things. A way I have seen this is that sometimes human isn't the first alternate shape they gain, and isn't their goto first choice most of the time. 

If you have a nonhuman MC in a fully nonhuman world then why would they become human anyway? If there isn't a compelling reason to seek a human shape then it would be bad to shoehorn that shape in just to deal with humans. It really isn't much of a goto shape and there are plenty of ways to manipulate objects without human hands that are perfectly serviceable or even superior. The problem with this is that there is a point where not being in a humanoid world is going to get boring to readers and start to lose its appeal. There is only so long you can spend talking about animals running around a forest before you start to get bored with the story. Or you start varying the environment and specifically avoid anything like villages and cities for human-shaped people and it turns into a situation where you are stretching to describe all sorts of alien environments for different forms and you run into believability issues and immersion issues. People just don't believe that your spider city is going to be like it is because it seems to be "human-shaped, with a twist for 8 legged freaks" and that feels contrived; or else it feels like its just not the real way a spider city would be and it should be different. Arguments will abound and people will not really like it. 

Most authors default to a human-shaped MC because eventually, you need some level of relatability, and unless you are writing for the furry crowd, it is hard to relate to nonhuman forms. So, while you can write a nonhuman MC, it does present a specific set of challenges that eventually threaten to overwhelm the appeal of the story. At which point you tend to gain more narrative benefit by granting a human shape that you lose by withholding it. 

It seems there are some pretty mixed opinions. I take that generally, it is acceptable, but needs to keep to what the fic is all about and that most people will result in doing so. I'll keep this in mind. Thanks for your feedback. To show my appreciation here's some rep!  

I possess a non-human protagonist in the form of a magi-genetically designed cannibalistic monster who's blood functions as an infection vector for baseline humans that can't afford the proper health packages, but should be still sort of adjacent to humanity (similar enough morphology, just with added in-built psychopathy and a constant urge for flesh and other biomass).

As for more characters who diverge even farther from the human norm ruining the story...well, that is both a subjective and skill issue. Subjective in the sense that readers who like and strongly identify with human protagonists won't get the same level of enjoyment from the work. Skill issue in the sense that how the character acts, the choices they make, and the general traits or attributes they possess, be in personality or physicality, is demonstrated and presented to the reader in a satisfying manner can go a long way into alleviating this.

Consider a story such as Children of Time by Adrian Tchaikovsky, for instance, in which the giant hyper-intelligent spiders are probably more interesting and more empathic than most the human cast, and you might find gulf between humanity and inhumanity is not so insurmountable, but actually territory ripe for exploration. Actually, Tchaikovsky is good at this in general. He has several novels that demonstrate the humanity of non-human protagonists, such as Dogs of War in which you follow a uplifted 7-foot tall dog-man with enough firepower embedded to make a Space Marine nod while weeping tears at the heresy as they find themselves honor bound to kill the abhuman abomination or die trying.

In summation, the ontology of your rarely ruins your story. Indeed, it might even elevate it.