Purebloods form the lowest caste of yuan-ti society. They closely resemble humans, yet a pureblood can't pass for a human under close scrutiny because there's always some hint of its true nature, such as scaly patches of skin, serpentine eyes, pointed teeth, or a forked tongue. Wearing cloaks and cowls, they masquerade as humans and infiltrate civilized lands to gather information, kidnap prisoners for interrogation and sacrifice, and trade with anyone who has something that can further their myriad plots.
However, the few nations that do not delve into sacrifice use these purebloods as ambassadors, letting them discus issues with other kings and noblemen in the affairs of their kind.