sorry for the long wait! here's your guys!
was thinking that they're a sort of nature guardian spirit. each one is born with a unique mask made out of a varying material (shown here are painted bone, wood, tiger's eye, ceramic, and obsidian) and are considered the heart/soul of this creature. it can be removed, causing the creature to shift into a human, but doing so leaves the mask vulnerable to damage/theft.
their horns molt in the summer, and they have different summer/winter coats. there's probably some genetic variation between them regarding horns/coat colors as well.
feel free to change whatever you'd like!!