Hello, Lioden!! I decided I wanted to try and suggest a mutation idea, so sorry if this has been done before... but.. WINGED CATS!! [Or just, stretchy skin cats]

"But, Cold... That's way too unnatural. Cats can't fly-"

Obviously. But 'winged' cats can't /actually/ fly. Instead, it is a mutation that causes a wing-like growth on the back of the feline. There are at least 28 documented cases with physical evidence and a growing number of photographs and videos!

According to Wikipedia: Cutaneous asthenia is a skin disorder caused by a collagen defect. Collagen is the protein that binds the cells of the dermis together. It is also called dermatoproxy, hereditary skin fragility or cutis elastica ("elastic skin") and is found in humans, cats, dogs, mink, horses, cattle and sheep. In cattle and sheep, it is called dermatosparaxis ('torn skin'). The skin is also abnormally fragile. The skin flaps peel or slough off very easily, often without causing bleeding. This explains why cats with the condition suddenly "molt" their wings.
LINK: https://en.wikipedia.org/wiki/Cutaneous_asthenia

This won't be a LETHAL mutation, as it's been continually proven that these animals live perfectly normal lives- other than the floppy wings on their back.

I'll probably add more when I think of it!! Thank you for reading >:D