Intellect Devourer (CR 6)

Small Aberration
Alignment: Often chaotic evil
Initiative: +4 (Dex); Senses: Listen +8 and Spot +9
Languages: understands Undercommon but cannot speak unless in possession of a body

AC: 17 (+1 size, +4 Dex, +2 natural), touch 15, flat-footed 13
Hit Dice: 6d8+12 (39 hp); DR: 20/magic
Fort +4, Ref +6, Will +6
Speed: 40 ft.
Space: 5 ft./5 ft.
Base Attack +4; Grapple -5
Attack: 4 claws +6 melee
Full Attack: 4 claws +6 melee
Damage: Claw 1d3+1
Special Attacks/Actions:
Abilities: Str 13, Dex 19, Con 15, Int 12, Wis 12, Cha 10
Special Qualities: electricity resistance 15, fire immunity, psionics, body-thief, protection from evil vulnerability
Feats: Alertness; Skill Focus (Perform)
Skills: Climb +10, Jump +9, Listen +8, Perform (act) +8, and Spot +9
Advancement: 7-8 HD (Medium-size); 9-12 HD (Large)
Climate/Terrain: Temperate and warm hill, mountains, and underground
Organization: Solitary or pod (2-4)
Treasure/Possessions: 1/2 coins; double goods; standard items

Source: Psionics Handbook

An intellect devourer charges into melee combat after first manifesting schism, allowing the creature to make a free partial action each round in addition to its normal round of actions. It must use that partial action to manifest a psionic power or use a psionic attack mode.

Psionics (Sp): At will -- compression, domination, invisibility, lesser body adjustment, painful touch, and schism. These abilities are as the powers manifested by a 16th-level psion.

Attack/Defense Modes (Sp): At will -- ego whip, id insinuation/empty mind, intellect fortress, thought shield.

Body-Thief (Sp): When an intellect devourer overcomes a lone victim, it consumes the brain and enters the skull (compacting itself if necessary with compression). Once in place, it organically animates the body as if it were the original brain and can use all its psionic powers on the possessed body as if its own (such as using lesser body adjustment to heal the grievous head wound). The body is a bit stiff but as long as the victim was not truly dead (hit points reduced to -10), the intellect devourer controls it completely. The theft lasts a maximum of seven days, after which time the intellect devourer must burrow out and seek more nourishment.

A possessed body's ability scores become those of its controlling intellect devourer, although its AC is unchanged. It has a maximum of 6 hit points (even when fully healed) and a base attack bonus of +4. The intellect devourer cannot use any of the victim's former special abilities, if any.

Protection from Evil Vulnerability (Ex): An intellect devourer is treated as a summoned creature for purposes of a protection from evil spell.

Skills: When it consumes a brain, the intellect devourer absorbs some of the victim's memories, gaining a +5 competence bonus on Perform (act) when trying to pass off the possessed body as the original.