"The Yuan Ti of Najara make deals with dark forces to keep their power. They would rebuild the empire on the backs of the dead, for they have the power to dominate, and the cruelty to rule." -Tahli
The Yuan Ti emulate the ruthlessness of their dragon neighbors; the fang is their symbol. In the past, Yuan Ti grew wealthy and powerful by exploitation of others and the resources of the land.
Their main source of power is necromancy. The Yuan Ti control a vast workforce of tireless undead to mine, farm, and dredge the seas and riverbeds for food and dragon bone. Najara and Athas are lands of battle, and the Yuan Ti have no end of fresh dead to resupply their army. This makes attacking the Yuan Ti a demoralizing undertaking.
The Yuan Ti first made deals with the powerful rakshasas; ruthless and corrupted devas who offer great power at a terrible price. The Yuan Ti soon became adept at deadlier forms of magic, and their willingness to use their magic made them even more formidable. The Yuan Ti are ruled by a lineage of serpent kings. Master propagandists, the Yuan Ti have claimed dragon ancestry in order to connect their lineage to the power of the ancient dragons, which has given them another psychological advantage over the masses within their subjugated territories.
The undead armies of the Yuan Ti come from an assortment of races and lands. The masses in the army are usually just left in the clothing they died in. The undead kept close to the capital city are dressed appropriately in uniforms pleasing to the eye. The bodies of the palace zombies are kept well preserved through powerful necromancy, while the rest of the undead army is left to rot.
The magic of the Yuan Ti is about warping the body, whether through shapeshifting or through modification after necromancy. They loathe mankind, whom they consider animals on par with their attack baboons. It is said that the Yuan Ti's cruelty comes from their resentment of the humanity they lack. The Yuan Ti are also versed in powerful venoms and poisons that can kill an elephant with a mere pinprick.
Slave magic consists of elementalism and shamanism. They worship the power of the lands and are secretly attempting to contact their ancestors, who lived in a time when the Yuan Ti could be defeated. Their magic is also based in making themselves more powerful. Strength, growth, and healing magic help them survive the tyranny of their superiors and give them value in the mercantile world of the Yuan Ti.
The rakshasas wield the most aggressive and dangerous magic among the Yuan Ti, with swirling darkness and powerful spirits of the dead. Their magic is the kind that lays waste to swaths of land or reduces an army to dust. They summon horrors and abominations that swallow cities and devour legions.
The Yuan Ti call the rakshasas demons, and the similarities between them are many. They come in a variety of shapes, sizes, and demeanors - short, squat, and wingless to immensely powerful, huge, and bat-winged. The knowledge of how to call and bind them comes from the dragons of old, who left out the binding spell in order to coerce more tribute from desperate wizards, who foolishly summon rakshasas without forethought. The Yuan Ti reside in large city temples, necropoleis, and pleasure palaces that dot their domain.