Yunkha were told by their creator goddess Yun
that the snake, an apex predator is the pinnacle of evolution. They worshipped snakes, and the more snake-like a Yunkha was, the higher they were in the social structure of most Yunkha societies.
Yunkha look like medium sized snakes, or partially like snakes, as they still retain limbs sometimes.
There is a societal structure of castes and nobility found in almost all Yunkha societies, that favours those who look more like snakes, over those with more human looks.
Disclaimer: For ingame stats, use the Yuan-Ti race and monsters from Volo's Guide to Monsters and the Monster Manual of D&D 5e, by WOTC