So the cool thing about urban fantasy is the way mythical creatures can be present in the modern world- and there's such a variety of creatures in myth and folklore that invariably some get short shrift. I mean we can all name dozens of books probably that have vampires, werewolves, and the fae. And lots of other creatures show up too, but there are some that I have not seen a lot of. Now I'm fairly new to urban fantasy so some of my picks might be more prevalent than I'm aware of- and by all means, if you have suggestions I'm all ears! But this is a list of creatures I'd like to see more of, especially in UF.
Brownies/ boggarts - the idea of a little house fae has so many possibilities. In folklore they would help the inhabitants but be careful not to abuse them. And boggarts are commonly an evil version of brownies, or perhaps a crazed brownie gone awry. They're also been known to inhabit marshes and devour those who go astray- I can see a boggart and a will-o-wisp acting in concert.
Elementals - one of my favorites are elemental spirits. Creatures from an elemental plane such as slyphs from the plane of Air, undines from Water or salamanders from Fire. They might be intelligent or mindless, hostile or not hostile, but possibilities are endless. Would a wind walker be invisible? Could there be a rift to elemental Water at the bottom of the sea, or an enchanted pond?
Merfolk - many of my readers know I have a thing for merfolk. The idea of beings living under the sea has always fascinated me. I know for me, standing by the ocean or a lake at night, with the waves rolling in and the moon high overhead, it's not hard to imagine a creature rising from the depths and coming ashore. Merfolk could be indifferent or rapacious (not friendly- that's no fun) and the deep sea could be full of them, or perhaps some shamble ashore in the dead of night to take humans, producing -gulp- hybrids. A pleasant idea.
Will-o-wisps - I'm big on these too. The idea of witchlights drawing a traveler to their doom in a marsh or bog is fun. I like the idea of wisps being creatures that feed off the life force of their victims- as the victim cries out and struggles the 'wisp grows stronger. I don't remember reading much of will-o-wisps but could always use more!
Sprites/ pixies - part of the fae, but there are so many variations. Some are depicted as small humanoids with wings, others as more insect- like and alien. All are pretty different from humans and should never be taken lightly.