Mind Flayer Alhoon (CR 18)

Medium Undead (Augmented Aberration)
Alignment: Lawful evil
Initiative: +10 (+6 Dex, +4 Improved Initiative); Senses: darkvision 60 ft., Listen +29, and Spot +29
Languages: telepathy 100 ft.

AC: 29 (+6 Dex, +5 natural, +4 mage armor, +4 deflection), touch 20, flat-footed 23
Hit Dice: 20d12 (130 hp); DR: 15/bludgeoning and magic
Fort +10, Ref +16, Will +23
Speed: 30 ft.
Space: 5 ft./5 ft.
Base Attack +12; Grapple +12
Attack: Tentacle +19 melee; or touch +18 melee touch; or spell +18 ranged touch
Full Attack: tentacle +19 melee and 3 tentacles +19 melee; or touch +18 melee touch; or spell +18 ranged touch
Damage: tentacle 1d4 plus 1d8+5 negative energy, or tentacles 1d4, touch 1d8+5 negative energy plus paralysis
Special Attacks/Actions: Extract, fear aura, improved grab, mind blast, negative energy touch, paralyzing touch, psionics
Abilities: Str 10, Dex 22, Con -, Int 22, Wis 21, Cha 26
Special Qualities: immunity to cold, immunity to electricity, immunity to mind-affecting spells and abilities, immunity to polymorph, SR 37, turn resistance +4, undead traits (Mind Flayer Lich 12th-Level Sorcerer)
Feats: Alertness; Combat Casting; Craft Wondrous Item; Improved Initiative; Spell Penetration; Weapon Finesse; Weapon Focus (tentacle)
Skills: Bluff +16, Concentration +28 (+32 casting defensively), Craft (alchemy) +17, Diplomacy +20, Disguise +8 (+10 acting in character), Hide +22, Intimidate +18, Knowledge (arcana) +26, Knowledge (dungeoneering) +18, Knowledge *the planes) +14, Listen +29, Move Silently +22, Search +20, Sense Motive +21, Spellcraft +20, Spot +29, and Survival +5 (+7 other planes)
Advancement: By character class
Climate/Terrain: Underground
Organization: Solitary
Treasure: Standard plus possessions (see below)

Source: Lords of Madness

This creature possesses the thin, spidery build and squirming face-tentacles of a mind flayer, but its flesh is dry and cracked, and its pale, white eyes emit an abyssal red glow.

Alhoons, or illithiliches as they are sometimes known, still seek our brains, even though they no longer need them for sustenance.

Augmented Subtype

A creature receives this subtype whenever something happens to change its original type. Some creatures (those with an inherited template) are born with this subtype; others acquire it when they take on an acquired template. The augmented subtype is always paired with the creature's original type. For example, a wizard's raven familiar is a magical beast (augmented animal). A creature with the augmented subtype usually has the traits of its current type, but the features of its original type. For example, a wizard's raven familiar has an animal's features and the traits of a magical beast.