Cerebrilith

Scrawny Brutes.  Cerebriliths were tanar'ri demons of incredible physical strength and dangerous mental acuity. The Abyssal natives possessed potent psionic powers in addition to their fearsome fiendish ones. Cerebriliths were hulking, monstrous humanoids, with frames suitable for ogres. When standing upright, typically done for battle, they stood about 8 ft (2.4 m) tall, but their hunchbacked forms meant they normally used their gnarled, clawed hands to knuckle-walk on all fours. 

Seamlessly fusing into their arched backs were their bulging, stretched-out skulls, which housed their most obvious feature a shockingly swollen and exposed brain, glistening wetly beneath a lattice of spinal bones. Their misshapen heads had round black eyes beneath their protruding, bony brows and long, thin tongues that flickered past their fangs, their jaws jutting out like separate appendages. The remainder of their bodies were gangly, their skin slick and slimy as if it continually leaking fluid.

Feasters of Knowledge. Cerebriliths spent their spare time training and cultivating their mental powers, usually by hunting mortal prey. They loved to kill intelligent beings to expose and extract their brains, which they would examine in an effort to gain fresh insights into the powers of the mind. They were also known to use their powers of mental domination in larger schemes, such as to mentally control a mortal community.

Potent Fiendish Minds. Cerebriliths possessed all the standard magical powers and resistances of a tanar'ri demon, being able to communicate telepathically and summon another of its kind or several dretches (up to two dozen) once per day. They also had access to the usual spell-like abilities of the tanar'ri. However, they complemented these with an array of innate psionic powers of the telepathy discipline, which allowed them to cause mental damage as well as read and dominate minds. In addition, only magical methods of attack could truly hurt a cerebrilith, with others only wounding them half as much as they normally would.

Combat. For the sake of getting to their brains, cerebriliths stopped at nothing to slay intelligent targets. The psionic demons opened battle with an assault of telepathic powers, often a barrage of ego whip and id insinuation attacks. When in melee range, they fought with their teeth and claws, attacking with brute strength while concentrating to gather more psionic focus, allowing them to strike with more power and accuracy.

Miscellaneous. Cerebriliths only joined demon armies when needed, serving as specialists to deal with specific psionic individuals and creatures. Otherwise, they engaged in their typical staking behavior alone or in small gangs of up to four. The illithid, otherwise known as mind flayers, deity Ilsensine could send cerebriliths (as well as  succubi and mariliths) in response to planar ally spells. Cerebriliths had keen senses of sight and hearing.

History. In the Year of Rogue Dragons, 1373 DR, the Zhentarim of the Citadel of the Raven summoned a cerebrilith to control and dominate the emerald dragon Vercevoran, who was kept captive in a castle at Hulburg on the Moonsea. The cerebrilith remained disguised beneath a great cloak and hood. On Mirtul 2, Pavel Shemov and Will Turnstone came to rescue Vercevoran, but were surprised by the cerebrilith, who commanded the dragon to attack them. As Will lured Vercevoran away, Pavel battled and finally slew the cerebrilith.