Yuan-ti are a race of serpentfolk that look like monstrous snake-men. They are usually evil and have their own language. Yuan-ti have a healing factor, can hibernate if necessary and have a quick adaptation to any new areas for survival. They can also emit poisons and hold their breath underwater for a significant amount of time.
The goal of the yuan-ti is to be dictated by their demonic god, Merrshaulk and to bring complete chaos to the world. The yuan-ti, despite their love and chaos have a rigid caste system with slaves at the bottom and purebloods take on the role as builders, artisans, spies and ambassadors. Halfbloods are warriors, mystics, enforcers, judges, generals, philosophers and can also lead a yuan-ti nest.
Males are barely favored in yuan-ti society, as only males can be high priests. However, they are too intelligent to not utilize their females' talents, and in non-priestly or reproductive roles females are allowed to do everything that males are. Female purebloods are often useful as seductresses in the human world.
Yuan-ti often inhabit subterranean places, usually places already constructed by other races since due to a lack of hands can have problems building. They may even decide to live in natural caves, or even build large tunnels under cities of other races. Yuan-ti fill their lairs with narrow corridors, too small for any race except snake-like ones and they will set up traps.
Way before humans ruled over Faerun, the rulers of Abeir-Tori were the Creator Races. The sarrukh, a reptillan Creator Race were one of the races to build huge empires. They bred the first yuan-ti by magically experimenting with and breeding men with snakes. The same way allowed them to create the naga, and then the lizardfolk process was similar to these. They eventually fell from power and the resourceful yuan-ti rose up to take over their Creators' power vacuum, even while sustaining the empire of Mhairshaulk. Of the fragmented World Serpent deity that the sarrukh had worshiped, the yuan-ti venerated the strongest aspect, a cruel and despotic deity, Merrshaulk, who grew far and aloof.
As the power of the yuan-ti became less seen in Faerun, and they instead started spying on human and demihuman through their organization and long-sighted plans. Merrshaulk had sunk into a deep sleep, ignoring his followers. Around the time of Netheril's collapse, Merrshaulk was reborn as a winged chief god, Sseth who became the main yuan-ti deity. In the end though, Sseth too sunk into a deep sleep.
At this point some sarrukh, long suffering a heavy war on other planes or sunken in hibernation in their ruins, began to return in some numbers. They needed Sseth's help badly but because of his deep sleep, he refused to answer prayers. So for assistance in their endeavors some of the sarrukh made a deal with the Mulhorandi deity Set, that put Sseth into a deeper sleep but allowed Set to assume Sseth's mantle and grant the sarrukh their much needed aid. Most yuan-ti do not even know of this transaction, though now Sseth struggles at his bonds some are being made aware of it.