Nightmare speakers were yuan-ti halfbloods with a humanoid head and upper body and a serpentine lower body. They were always female.
Nightmare speakers were among the cruelest of the yuan-ti, and they delighted in torturing prisoners and slaves, keeping their victims in a state of constant dread and fear.
Like other yuan-ti, nightmare speakers had many odd natural abilities. They were immune to poison and resistant spells and other magical effects. At will, they could turn into a medium-sized snake (or back into their natural form), although any equipment they carried was not also transformed. They could use bring negative energy to bear against opponents twice each day.
Yuan-ti nightmare speakers could innately cast the spells animal friendship at will, though only with snakes, and suggestion thrice each day. They also knew the cantrips chill touch, eldritch blast, mage hand, message, poison spray, and prestidigitation, as well as the spells arms of Hadar, darkness, fear, hex, hold person, hunger of Hadar, and witch bolt; however, they could only cast a total of two spells each day.
Additionally, nightmare speakers could reach into the nightmares of any creature within 60 feet (18 meters) of them that they could see, and create an illusory manifestation of that creature's deepest fears. The illusion was immobile and visible only to the targeted creature, which could be damaged and frightened by the illusion if they thought it was real. The nightmare speaker could maintain the illusion for up to 1 minute but had to concentrate to do so.
Nightmare speakers wielded scimitars in combat. They could also use their lower body to constrict an enemy, slowly suffocating them. However, they preferred to terrify their opponents rather than kill them.
Yuan-ti nightmare speakers were "priests" of a sort, who made pacts with Dendar in exchange for power. They fed their patron fears and nightmares from the Material Plane, and received nightmarish visions from her. They interpreted these visions as prophecies and did their best to make the vision come true.
Nightmare speakers would manipulate humanoid communities in order to acquire more victims to torture and terrorize. They were also known to enjoy the company of undead.