TL:DR = trolls exist, troll cells are universal stem cells on steroids, specifically bred trolls are more powerfull and used to fuse different animals together with their regenerative properties.
In this world there are people, all the types of ethnicities and more, a lot of people...
but the races list doesn't stop there. A long time ago a very curious student started studying the regenerative capacities of Paranthropus Troglodytus also commonly known as mountain trolls, it was already widely known that the skin and bone cells from a troll's body could regenerate injuries if grafted into other species, but he managed to breed a race of trolls which had more powerful regeneration and their cells could cause people to fuse with other species.
From the experiments he came with bestial creatures by grafting limbs of an animal onto the body of another, based on the limb grafted and sex of the animals the end result was different.
For example, for male dogs who's eyes were removed and implanted into a female horse, the end result would be a shorter horse with a more canine figure and sharper teeth, but if the sexes where switched then the result would be a horse who grew a second pair of wolf ears and a furry pelt on their skin, with claws instead of hooves. With just two animals, the options are infinite but then he also discovered that the process could be repeated on the same creature mixing chimeras with more than one animal or chimeras with other chimeras. The mad student also discovered that chimeras were fertile and could reproduce with their original species if they were not too ''modified'' and they could also breed with other identical chimeras of the same type.
Some religions were horrified by the discovery and the student had to run for his life before being burned alive for demonic creations, he escaped and was employed by a dictator to raise an army of perfect creatures.
After a few decades the student was long dead of old age and his techniques for chimera creation became public, the civilians now used to chimeras being a normal thing started experimenting on themselves to change their bodies the same way a teenager would do by getting tattoos or piercings. After some centuries, this practice created a myriad of intelligent chimeras with different cultures around the world.
What is my question?
Does my explanation for why chimeras exist in my world have any merit and could be plausible or realistic if some science was applied to it?
What qualifies as a good answer?
This is a straight forward yes or no question, but obviously a reason and explanation for what limits this idea to magic and why it can't be possible in a scientific world is needed, or if it is a yes, an explanation on how come my very simplistic explanation could work.
-If anyone might find this idea interesting and wanted to use this in their project, feel free to take it, steal it and make it your own, I'd be flattered. I don't really know law but a quick google search says ''As soon as you record an idea, for example by writing down the outline of a story, it's protected by copyright. As long as the work is original, copyright protection is automatic'' Well take it as an official statement, I don't care about copyright, use any of my ideas as you wish. I go by the philosophy that competition breeds excellence, if you think you can do a good work by taking concepts from my projects, then you deserve all the rights to use them, this one question might interest you or might not, but I'm sure I will post some more interesting stuff in the future.