Eeeeeevil!
Overseer (Half Fiend Mind Leech)
Fine Outsider (Evil, Symbiont)
Hit Dice: 1d8+1 (5 hp)
Initiative: -2
Speed: 1 ft.
AC: 21 (+1 Natural, +8 Size, -2 Dex), Touch 16, Flat Footed 17
Base Attack/Grapple: +0/-19
Attack: Bite +5 Melee (Attach)
Space/Reach: 1/2 ft./0 ft.
Special Attacks: Attach, Darkness 3/day (CL 1), Mind Blast, Psionics, Smite Good
Special Qualities: A/C/E/F resistance 10, DR 5/magic, Darkvision 60 ft, Immunity to poison, symbiont traits, SR 11, telepathy
Saves: Fort +1, Ref -2, Will +6
Abilities: Str 5, Dex 7, Con 13, Int 20, Wis 14, Cha 18, Ego 23
Skills: Concentration +5, Hide +14, Knowledge (Any two) +9, Listen +6, Move Silently +6, Sense Motive +6, Spellcraft +9, Spot +6
Feats: Alertness (B), Iron Will, Spell penetration (B)
CR: 1 or base creature +3
Attach (Ex): If an overseer hits with its bite attack, it burrows into the target's flesh and makes its way to the brain stem. Since the bite deals no damage and the leech secretes an anesthetic, the host is often unaware it has been bitten until the overseer has established itself at the seat of the host's central nervous system.
Mind Blast (Su): This attack is a 60-foot cone. Anyone caught in this cone must make a Will save (DC 19) or be stunned for 1d4 rounds. Each time the overseer uses this ability, it deals 1 point of intelligence damage to the host. An overseer without a host cannot use this ability.
Psionics (Sp): At will - charm monster, detect thoughts, dominate person, and suggestion. These abilities are as the spells cast by a 10th-level sorcerer (Save DC 14 + spell level). Each time the overseer uses its charm monster or suggestion power it deals 1 point of intelligence damage to the host. Using its dominate person ability deals 2 points of intelligence damage to the host. An overseer without a host cannot use these abilities (though it can use detect thoughts).
Telepathy (Su): An overseer can communicate telepathically with its host, if it has a language.
Skills: An overseer has a +4 bonus on Move Silently checks.
*Ego: just like magic items (Will 23 or be controlled for a whole day)
Or just use a normal Mind Leech...