Cerebrilith

A cerebrilith was a type of tanar'ri demon native to the Infinite Layers of the Abyss that possessed psionic powers in addition to its fiendish ones.

Description
A cerebrilith was a huge and monstrous ogre-like humanoid creature. When standing upright for battle, it was around 8 feet (2.4 meters) tall, but it normally knuckle-walked on all fours, owing due to its hunched back. This was to support its massive, bulging, and stretched-out skull, which merged into its hunched back. This housed the cerebrilith's most obvious feature—a shockingly swollen and exposed brain, shielded beneath a lattice of its spinal bones. The hideous face had a bony brow and protruding fanged jaw with long, thin tongue. The remainder of its body was relatively gangly, with skin turned slick and slimy as if it continually leaked some fluid.

Behavior
Cerebriliths spent their spare time cultivating their mental powers, usually acting alone or in gangs of up to four, by hunting and killing mortal prey. They loved to kill intelligent beings and expose and extract their brains, which they would examine in an effort to gain fresh insights into the powers of the mind.

They only joined demon armies in specialist roles to meet specific purposes, such as to a slay a mortal psionicist or psionic creature.

They could also use their powers of mental domination in larger schemes, such as to mentally control a mortal community.

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.

Powers
Cerebriliths possessed all the standard magical powers of a tanar'ri demon, being able to create deeper darkness, desecrate or create an unholy blight over an area, detect and dispel good powers, create a magic circle against good, and transport themselves as if with greater teleport, all as often as they pleased. They had the same resistances: immunity to poison and electricity, resilience to acid, cold, and fire.

However, they complemented these with an array of innate psionic powers of the telepathy discipline, causing mental damage, mind-reading and domination. They could daze and damage a mind with brain lock and ego whip, and instill confusion with id insinuation at will. They could also detect psionics at any time. Thrice a day, they could attempt to control a mind with psionic dominate, read one with mind probe, and protect themselves with ectoplasmic form. Once a day, they could deliver a powerful mind thrust to damage the mind directly.

It could also communicate via telepathy, but this was common to all demons.

A cerebrilith could, once a day, attempt to summon another of its kind or up to two dozen dretches.

They had keen senses.

Combat
These psionic demons opened battle with an assault of telepathic powers, often a barrange of ego whip and id insinuation attacks. When in melee range, they fought with teeth and claws, attacking with brute power but with psionic focus on striking unerringly and dealing more damage.

Relations
The illithid deity Ilsensine could send cerebriliths in response to planar ally spells.