Based on a grell, with a twist.
Gloomflayers
Large Aberration (Extraplanar)
Hit Dice: 12d8+60 (114 hp)
Initiative: +9
Speed: fly 60 ft. (perfect)
Armor Class: 19 (-1 size, +5 Dex, +5 natural), touch 14, flat-footed 14
Base Attack/Grapple: +9/+19
Attack: 2 tentacles +14 (1d6+6 plus paralytic toxin)
Full Attack: 2 tentacles +14 (1d6+6 plus paralytic toxin), bite +9 (2d6+3)
Special Attacks: paralytic toxin, mimicry, bioluminescence, absorb spell-like abilities, improved grab
Special Qualities: blindsight 60ft, immunity to electricity, mind-affecting effects, spell resistance 21
Space/Reach: 10 ft./10 ft.
Saves: Fort +9, Ref +9, Will +8
Abilities: Str 22, Dex 20, Con 20, Int 18, Wis 10, Cha 8
Skills: +2 Spellcraft, +2 Use Magic Device
Feats: Combat Expertise, Combat Reflexes, Improved Counterspell, Improved Initiative, Magical Aptitude
Environment: warm caves, volcanic regions
Organization: solitary, pair, or brood (3-6)
Challenge Rating: 10
Treasure: double standard
Alignment: N
Advancement: None
Level Adjustment: None
Blindsight (Ex): Gloomflayers have no visual organs but can ascertain all foes within 60 feet, possibly using sound, scent, and vibration, or some other hitherto unknown sensory organ.
Paralytic Toxin (Ex): A creature hit by a tentacle must succeed on a DC 21 Fortitude save or be paralyzed for 1d4 rounds. The save DC is Constitution-based.
Mimicry (Ex): A gloomflayer can perfectly mimic the sounds of creatures within a 60-foot radius. This is a free action.
Bioluminescence (Ex): A gloomflayer can emit a blinding flash of light as a standard action. Creatures within a 30-foot radius of the gloomflayer must succeed on a DC 21 Fortitude save or be blinded for 1 round. The save DC is Charisma-based.
Absorb Spell-Like Abilities (Su): A gloomflayer can absorb spells and spell-like abilities as a standard action upon consumption of a brain. It must make a successful opposed Intelligence check (DC 10 + the caster level of the spell) to absorb the spell. The gloomflayer can then use the absorbed spell-like ability as its own, expending a use of its absorb spell-like abilities ability. The gloomflayer has a pool of spell-like abilities equal to its Intelligence modifier (4 random spells/spell-like abilities, 4 uses per day).
Improved Grab (Ex): To use this ability, a gloomflayer must hit a Large or smaller creature with both its tentacle attacks. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it attaches to the opponent’s head and can constrict.
Constrict (Ex): A gloomflayer deals 1d6+8 points of damage with a successful grapple check.
The monster of nightmares, the gloomflayer is an ever-present danger in the depths of the Evergloom resembling a giant brain with long tentacles, floating effortlessly through the air via some unknown means of propulsion as it silently stalks its prey. In addition to prehensile tentacles, it also wields thinner tentacles that hang down with paralytic toxins in tiny stinger needles to ensnare its meals. They also have an uncanny ability to mimic sounds such as clicking and whistling, and use their bioluminescent light to flash and dazzle smaller prey unused to such bright illumination.
Worse, there have been documented cases among the Ebynai of gloomflayers absorbing magical and psionic abilities, gaining even the ability to wield certain magical items through telepathy.
Breeding consists of eggs attached to the ceiling over a breeding pool. When the hatchlings emerge, they drop into the pool where a live but paralyzed victim waits to be devoured by the new gloomflayer spawn.