Endonym: Apeshi
Apep was the spiritual guardian of a long dead royal family of a forgotten sand kingdom. Apep was tasked with protecting them from the horrors of the night by devouring the chaos. However, Apep was overwhelmed, and engorged himself on his prey in an attempt to protect his family. Apep succumbed to the darkness of the Abyss, turning into a colossal, bloated serpent.
Some citizens of the sand kingdom took to worshipping Apep’s new form, abandoning their old Gods, whether it be out of fear, admiration, or by might. These followers took to dark magics to undergo a similar metamorphosis, in order to more closely resemble their deity. Using dark chaotic energy from the Abyss, they transformed themselves into what would become the Yuan-Ti today. In their quest to grow closer to their God, it seems they have given up some shard of their sanity, to be more like the chaotic, primal beast that is Apep.
They still have a fully formed society, but the members of such are all wholly fanatical followers of Apep. Their cities are entirely shunned, exiled to live underground or else face total and utter annihilation. They have several rituals devoted to their God, many of which revolve around killing and sacrificing the unfortunate prisoners they find out in the world.
Life in Yuan-Ti society is like life in a secret organization, there are no friends, everyone is out for themselves and will do whatever they can to rise to the top, even if that means killing a family member. Yuan-Ti are heartless and calculated, however, the previous statements are not absolute, there are those Yuan-Ti who have broken away from their society to join the greater society above ground; such insolence is viewed as a weakness, and punishable by death.
There is one slight drawback to their transformation into snake-Human hybrids. Their minds are chaotic and every Yuan-Ti is doomed to go mad eventually, falling into the state of a rambling madman. It is advisable under Yuan-Ti society to execute those at the first sign their mind might be slipping into chaos.