When I invent creatures for my fantasy world, I use a few techniques to brainstorm ideas and polish them. I usually use the this one to polish ideas, but it can also be used to brainstorm new ones. Either way, one way to worldbuild new creatures for your world is to Fit the Niche.
As in, where in the world does the creature fit? Where does it live, what does it eat, and at what time of day? Does it hide in trees, or in the ground, or perhaps not at all? I like to carve out a niche for creatures I invent, finding reasons for why and how they would exist. As a biologist, I like my creatures to make sense, and am delighted when strange creatures find a special place in their imagined environment.
As I said, I usually use this technique to tailor a creature I’ve already thought up, but occasionally I start with this. In one case, I needed a predator for another creature I had created, a gecko-like creature with an interesting defense mechanism. I asked, what would a predator need to effectively hunt this creature? It would need to be fast–probably small, and very smart in order to outmaneuver the gecko’s defenses which play a part in the story. I liked the idea of the mongoose and the snake interplay, so I made it a mongoose/weasel-like creature, with powerful hind legs and a fluffy tail to disorient the gecko. This new creature was built entirely out of a niche that needed to be filled.
You can also create new creatures by changing the niche of already existing animals. What if you turned a hoofed animal (perhaps, say, an elk) into a predator? How would its body be different to enable it to effectively hunt? Would it have sharp, pointed hooves or longer teeth? Would its legs be more flexible to support crouching and pouncing, or would it have some other feature that would allow it to run down and gore its prey, like sharper antlers? (Now I have a creepy picture in my head of a saber-toothed sharp-antlered elk stalking prey with its head low through the brush…Reminds me of this moose.) Existing animals aren’t the only ones you can tweak. What if dragons were herbivores? What if unicorns were nocturnal and ate fish from the streams? How would their different niches change how they looked or acted?
Figuring out a creature’s niche can not only help your creature make sense to your readers and make your world more real, but it can also give you more ideas about how the creature might look or act when your characters encounter them. Which is, presumably, why you’re creating creatures in the first place. Unless you also like to draw strange things for no particular reason, like I do…but that’s another story.
Have you ever come across a book or movie that had creatures that didn’t make sense? Did it distract you from the story?