Yuan-Ti Pureblood

Yuan-Ti used to be human. They had a vast ancient civilization that was powerful and wealthy. They learned the cannibalistic rituals needed to gain “the aspect of the serpent” and promptly ate a bunch of their servants. With a now constant need for human sacrifices, they invaded their neighbors and were largely successful until one fateful battle where they were defeated so badly, that the opposing army was able to wipe out their entire civilization and drive them nearly to extinction. Their civilization toppled, the Yuan-Ti retreated to their fortified jungle cities, biding their time but still desperately requiring human sacrifices.

Most aspects of Yuan-Ti culture now revolve around the capture, sacrifice, and consumption of humanoid flesh. Simply put, they’re rarely nice neighbors to have. They’re ambitious, they work to destabilize governments and behind the scenes in countless positions of power. They dream of the time that their mighty civilization can return to prominence, like an unseen viper ready to strike.

On a more personal level, Yuan-Ti are widely considered emotionless and cold. They severed their connection to human emotions with their dark rituals. While they understand emotions on a logical level, however, they’ve lost the many passions of humanity. Other people are pawns to be used, and the self is the only thing that’s important. All of this is stacked on top of a fundamental xenophobia and believe the Yuan-Ti are the “true people”. Yuan-Ti regard everyone as dangerous threats, respectable fellow Yuan-Ti, or simply as food.

Yuan-ti Pureblood (Revised)

Purebloods form the lowest caste of yuan-ti society. They closely resemble humans, yet a pureblood can't pass for 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.
ability score increase: Your Charisma score increases by 2, and your Intelligence score increases by 1.
age: Purebloods mature at the same rate as humans and have lifespans similar in length to theirs.
alignment: Purebloods are devoid of emotion and see others as tools to manipulate. They care little for law or chaos and are typically neutral evil.
Size: Medium
speed: Your base walking speed is 30 feet.
Languages: You can speak, read, and write Common, Abyssal, and Draconic.
race features:
Darkvision. You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can't discern color in darkness, only shades of gray.   Innate Spellcasting. You know the Poison Spray cantrip. You can cast Animal Friendship an unlimited number of times with this trait, but you can target only snakes with it. Starting at 3rd level, you can also cast Suggestion with this trait. Once you cast it, you can't do so again until you finish a long rest. Charisma is your spellcasting ability for these spells.   Cold-Blooded. Magic affecting your mind is naturally less effective due to your emotionless state. You have advantage on all Intelligence, Wisdom, and Charisma saves against magic.   Poison Immunity. You are immune to poison damage and the poisoned condition.   Serpent's Sense. Yuan-ti's likeness to snakes has enabled their sixth sense; the ability to read major heat signatures. You have advantage on Wisdom (Perception) checks to detect warm-blooded creatures that are not obscured by anything. You cannot discern anything beyond number and size class through heat signature. 
Purebloods were described as human-like but with minor reptilian features, such as snake-like eyes, a forked tongue, and patches of scales on their skin. Purebloods had weights and heights in the same range as humans.