I’ll be upfront about it: I have a sucker button for fantasy biology.
I have a treasured copy of the 3.5 ed Draconomicon. I have various other monster sourcebooks, D&D and otherwise, and love to reread the sections on how monsters fit (or don’t) into the local ecology. Some books I haven’t held onto but have kept photocopies of various really-well-thought-out critters; Palladium’s psionic emirin is a particular favorite. (And probably part of where my bunnies get my cougar youkai from in MCO.) And when I poke around DeviantArt.com, I always look for different takes on classic beasties: chimera, seahorse, mermaid, and griffins to name a few. Bluejay griffins make everything better.
I love fantasy biology. Add an interesting bio aspect to a fandom, and my bunnies will be all over it. To name just a few – Ubel Blatt, Parasyte, Stargate, and now Kabaneri of the Iron Fortress.
(Yes, I’ve only written fic for two of those… so far. No, I haven’t seen Kabaneri yet. I’ve seen vid clips, and the fan wiki, and I have notes. Including thoughts that the Kabane infection isn’t just one virus, but a sort of slime critter that comes with a host of infectious viruses that are symbiotic to it…. Meep.)
Having that love of a subject critical to the story is important. Because getting all the way through a story is hard, and if you’re not slightly obsessed with part of your idea… it’s that much harder.
But with a passion for your subject, you have something to lean on. Something you can dig into and convey to the reader. Something that you can research the real-life basis for when you get stuck, hopefully giving the bunnies both enough of a breather and enough new ideas to hare off toward the end of the story. Because unless you get very lucky, at some point we all get stuck, and need some outside info to break the deadlock.
Right now I need to go get some inconvenient quirks of biology into Seeds. Oh dear….