Writing believable mythical species
Believable mythical species is a bit of an oxymoron. When you're writing a story with a mythical species, getting the balance between expecting your readers to suspend their disbelief and writing something just believable enough to be immersive can be tricky.
T.J. Klune's House in the Cerulean Sea is an excellent example of giving mythical species character. His dedication to showing the humanity of each species in the story is what makes each character shine. While the characterisation borrows from expectations, none of them are reduced to bland archetypes.
Giving your mythical species a personality, quirks and traits prevents them from being a blank model in your stories. It allows your reader to engage with them. Even the least sentient of creatures need a motivation. Without motivation, your readers won't believe their actions. If your giant angry sentient octopus antagonist is a grump just for the sake of it, because of course it is its a giant angry octopus, the character becomes less believable. Give it a personality, motives, fears.
Many writers use 'existing' fantasy species in their work. And why not! But the danger is lifting a creature out of one story and plopping it as is in their own story. This makes for some boring creatures and might lessen the believability if the style doesn't suit the story. A good parallel is dragons in Tolkien's work, dragons in Le Guin's work, and the beloved dragon in Klune's work. These are three very different sets of creatures, each with the same inspiration. A money-hoarding monstrous dragon would not have been a heart-warming addition to Klune's plot. Nor would it have provided the same political and philosophical discourse to Le Guin's. Each of these dragons are designed around the plot and world that they exist in.
Size is an important thing to consider in your books, even just for common sense physics. If you free the dragon in the heart ancient ruined castle, it is going to knock down some pillars on its way out. When an average human size character is talking to a giant, how have they positioned themselves to be heard? Or are they shouting up to them? Does a small creature interact with the setting the same way average human sized characters do?
If your world (or one part of your world) is as densely populated with a type of mythical creature as it is humans, consider how this will impact the setting and infrastructure. Create a world that expects the existence of mythical species. If half your cities population is a community sun drinking half-plant half-humanoid creatures, perhaps that city makes ample use of skylights in the building. Wouldn't a city that includes a healthy group of ambitious species have regulations on how many publicly funded water features there must be per square mile? When you're world building, create a world that expects the creatures that live in it. Unless the story deliberately takes a species out of its home environment, a nocturnal species not finding shelter from the sun in time just isn't believable and will be read as forced tension.
Note: some of the above could be considered allegorical for the experiences of people with disabilities in the real world. If this is your stories main purpose, feel empowered to explore that with all the respect and dignity afforded. If it isn't, you've created an entirely mythical world, why draw the line of realism at inclusive infrastructure?
If you're going down the route of creating your own mythical creature, be mindful of how you describe how they look. A creature with the head of a rabbit, legs like a lizard, the body of a cheetah and it had sharks teeth is certainly original, but might come across to your reader like the product of an after school club craft session. Think about your creatures purpose, the setting its usually found in and what features it might have evolved living there. Also, keep in mind that sometimes less is more. A new creature appearing on the scene shouldn't necessarily greet the reader with a paragraph of description of its appearance (unless you've found a writing style that this works for, perhaps a witty third-omniscient narrator who just has to make comments on everything).
Essentially, treat your mythical species as you would any other character in your book. Even if they're non-speaking or not sentient, your story's equivalent of a pet dog, they need to have a personality. The setting you create for them needs to be believable, or have a good reason why its not. Most importantly, they need to be consistent! Get in touch today to chat about how I edit fantasy species.