Fantasy roleplaying games are rife with fantastic hybrids and magical creatures. It's probably to be expected, since danger and risk are such critical parts of such a game, but virtually all of the fantastic creatures you find in the typical RPG dungeon or wilderness are of the huge, monstrous, and at least potentially aggressive variety. I've wondered at times, though, why the gods and wizards of fantasy worlds would limit their creations to big scary things. Yes, wizards often want powerful creatures for pets and guardians, and deities create monsters to inspire followers and frighten the faithless. Surely, though, in the long history of the average fantasy world, there would have been inquisitive but peaceful wizards whose interests in magical breeding and hybridizing were a bit broader than making owlbears to terrorize the non-magical populace.
Even among "normal" creatures, the ones that get statted up in RPGs are the ones that pose a clear and present danger to humans - the lions and tigers and bears (oh my!) A trek through a real world cave, ruin, or wilderness, however, would feature a
lot more little harmless things - rabbits, songbirds, mice, lizards,
frogs, garter snakes, squirrels. It's understandable that harmless creatures get short shrift in the RPG rulebooks. Stats are rarely or never necessary for them, but that doesn't mean they should never appear in-game. Just like terrain, vegetation, weather, and any other element of scene and setting, used well, harmless creatures add charm, atmosphere, and depth. And just as a setting can benefit from fantastic scene dressing, like talking statues, glowing pools, and shrieking mushrooms, it can benefit from the addition of a few fantastic but harmless creatures, too.
As I mentioned above, I've pondered this topic from time to time. A link to a page called Hex001, posted on Google Plus by Tim Shorts of Gothridge Manor, brought it back to my mind today. Included in this one-hex setting is a flying cat. Not a lion or a tiger, but an otherwise ordinary tabby with wings. True, it is given a stat line, but as a combatant it's pretty negligible. It's pretty much completely unable to threaten even a normal human, let alone a party of adventurers, and it can't do much for them in battle either. As a bit of campaign flavor, it's delightful. Where did it come from, and why does it exist? Is it the only one of its kind, or are there more out there somewhere? What is its niche in that one-hex mini-environment - does it swoop like a hawk to catch mice below, or does it chase birds on the wing? And what a cool mascot for the party lucky enough to befriend it!
My own initial inspiration, years ago, came from a little wooden ornament of a winged frog. Imagine a quiet pond in a remote valley inhabited by tree frogs with white feathery wings, flitting through the air in pursuit of flies. They're too small and fragile to fly over the icy peaks around the valley and escape into the wider world, but the druid who also calls the valley home sees that they are protected.
Fantastic harmless critters might be limited edition creations of a wizard, god, or spirit. They might be isolated sub-species, whether of natural or magical origin, as in the example of the frog pond above. They could be legendary, thought either to have died out or to be entirely mythical. Or they could be common and widespread in the campaign world, much like griffons, owlbears, and wyverns are considered to be in many settings.
The possibilities are limited only by imagination. You could easily have tortoises with bright plumage like tropical birds, or rodents with tortoise shells on their backs, lizards with retractable eyestalks, duck-billed pygmy deer that forage in muck, sheep with blue fleece, rabbits with ram horns, blind flightless birds that skitter about the floors of dungeons like mice, long-necked toads, water squirrels with sleek oiled coats and webbed toes, aquatic lemurs with fish tails (some evolutionary offshoot of the merfolk line?), carnivorous snails that spin sticky webs of their slime, furry snakes, rats with antlers, chickmice (hybrids with the heads of chickadees and bodies of mice, diminutive seed-eating cousins to the owlbear), little chimerae with the bodies of raccoons and heads of raccoon, rabbit, and lizard...