I have no use for centaurs. They don't really build cities or luxury items. They don't have dungeons. They do horse things or "savage things," and usually end up as barbarian raiders or the Hekawi, or the Joaquin Phoenixes of the forest in Harry Potter. But if I'm going to have a symbol of nature in my game it needs to be more terrifying than bronies, and for everything else I can just put a normal dude on a horse. I don't save money bundling them as a package. I don't get ideas that I can't just do with guys on horses.
I think the much reviled chevalle (Horse) is at least more of an idea. A centaur who can pretend he's a regular horse. There's an 80s action figure quality to this I appreciate. But he has a bigger bucket of game stats and an empty bucket of interesting things to do with him. Chevalles would be like your friend who thought dressing up in a gorilla suit was cool. How long would you let him do this before you took action? That's where you BEGIN with a chevalle in a world where centaurs are a thing.
So here's the move I made:
a) All centaurs are chevalles
b) They go the other way.
When we picture demons we give them the features and "super-powers" of animals and our own insecurities about our bodies, our insecurities, our mortality, our strangeness and grossness. As an afterthought we clothe them in the elemental nature of our world and its fears, in fire and stink and dark, ice, filth, dirt, lightning.
That's what horses do, too, and the worst enemy they have really is us.
Now, we are metaphorically ruled by our demons. Horses are quite literally ruled by theirs.
There is a thing that looks like a horse. It is not like them. We would never know it. Horses don't treat them differently because horses Know, but aren't smart enough to be sure, so they treat every horse as if they are the other things. They live among the horses. They watch them from afar, from outside humanoid society. And within, of course, because they are like horses, and we bring horses everywhere, even dwarf caves. Perhaps it is a literal demon that possesses the body of a horse but I prefer to think of it as something just strange, old, and Else, something we just missed because it's so good at being another thing.
It's smart. Scary smart. And it's protective of horses in the same way that a farmer is protective of his crop: it is sown and raised to be harvested, when harvested it will be destroyed, and the tender must profit from that destruction and sustain himself.
They are the Horsemen, and they tear their way out from horseflesh. The skin of the horse's face splits and peels off, taking much of the muscle, leaving a gooey skull and sockets that somehow see. Fingertips, humanlike and dextrous, peek from beneath the flesh fissure, grip the hide, and rip the hide, unzipping the horse like a banana. Long, impossibly lanky, muscular arms tear their way out, and a mighty man-like torso is dragged from the stump where the horse's neck once was, clawed and fleshless hands bracing against its own shoulders, pushing itself through the blood and organ fluid like a birth, or like Super Family Double Dare. The "peel" is torn away, leaving ragged strips, and the horrible figure does horrible things.
If you're lucky they'll just kill a horse that Knows and is Sure and threatens them. Or they might partially eat a few, or even lure them away with an intelligence attributed to rustlers, THEN Eat them. Or they may decide that a wrangler or horsemaster has wronged them or their crop. They may decide that an entire city has made their crop into slaves and winnows their meat with slave labor. They may not act directly themselves, but carry the secrets they hear as a 'dumb animal' to the enemies of THEIR enemies, and then sit back and enjoy the destruction and the free reign they are afforded to abscond with some farmer's crop of horses.
Centaurs exist to run and look impressive, the Chevalle was only ever an "Um Actually" centaur and we don't need YouTube comments in the Monster Manual. We need monsters. So I have one monster that is kind of two monsters I can't use, pretty much not, and also if I want to do any "Yes this is cultural appropriation but it's ok because they're ANIMALS!" stuff I'll just use Mongol stand ins or samurai stand ins or Blackfoot stand ins or Bedouin stand ins and skip the part where you can always see their huge genitals.
What I might do, though, as a half measure, on a random encounter table, is just put another animal on the animal end. Crocodile. Giraffe. Polar bear. This, incidentally, is what I usually do with mermaids. (Squid. Jellyfish. Seahorses. Leopard seals. Elasmosaurus.)