Yuan-ti are a race of snake people who have their origin in the Appalachian Mountains. They have 3 forms, "quarter blood" who look like humans with only a few snake-like features, "half-breeds" are humanoid snakes, and "true bloods" (outsiders call them abominations) which are snakes with human heads. The snake portion are that of the timber rattlesnake.

Cmbt Yuan-ti are nonviolent, but will defend their homes and families with their bites and mutations. Only those who live near trading communities tend to have weapon skills. That is because they try to spread their message to those passing through, and sometimes, the reached to dislike it in the extreme.
Hab/Soc

Yuan-ti have their beginnings 110 years before the Cataclysm. In the Appalachians, there was a church that took one passage of the Bible to an extreme. It had to do with serpents. During services they handed poisonous snakes of all types, and some muttering in tongues. It was a nusually fiery preacher who started the yuan-ti. He was true to his faith, but during a service, while muttering tounges, he had an affect on one of the younger boys in the groups. It is not known what he said, but the boy got the message that man and snake were equal to god. As he grew, he studied genetic engineering, trying to find a way to make a "perfect being". It took him decades, but he and several companions, created a "perfect being". It was the first half-breed. They had created several dozen before the Cataclysm. They were killed not even knowing that there was a major flaw in the yuan-ti genome, one that had saved them from extinction. They had 3 forms and the one farthest from reptiles allowed them to interbreed with humans and bring needed blood into the race. Now they act as their ancestors, a peaceful religion that tries to keep to themselves. The only exception are other snakemen. Some ophidians and hissers have joined them, but most of them meet the odd people with fear or anger. They have not expanded much from their original location, being found in West Virginia to Tennessee.

Derek

PS There is such a church and I do not mean to put them down in anyway,
shape or form