Oh man. If it exists in mythology, it’s usually real in my books. I might not mention every single mythological creature in existence, but I still have ideas about a lot of them.
I am on a demon kick too, since I just wrote about an exorcist. 😀
I regularly have the following monsters/races in my books: elves, fey, jinni, vampires (with my own spin), angel, dwarves, nymphs, dragons, mermaids, sirens, selkies, ghosts, spirits, demons, zombies, iara, kelpie, incubi, rusalka, nixies, naga, lamia, vila, apsara, samodiva, and yeah….I could go on.
Essentially I have a list of how these creatures/races are related to each other. It’s how I explain the similar creatures in various folklore. So for example, there’s a lot of water-horse-that-drown-you myths in Scotland and Ireland. So I just say they’re cousins of each other. 😀
It’s a lot of fun. I know, I am huge nerd. But I really like taking mythology and putting my own spin on things.