I'm not in the habit of designing prestige classes, so the PrC below is probably horribly horribly overpowered. Regardless, looking forward to review and comments. In particular, the high skill-rank requirements for the prestige class take into account an illithid's aberration levels.
Illithid Herd-Thinner (Prestige Class)
The mind flayers of Gyrus have adapted well to the logistical nightmare of keeping a massive illithid population fed. One of their more notable practices is the establishment of a large and elaborate system of 'wild game preserves' on the surface -- large populations of 'wild' humanoids that are not truly enthralled en masse, but kept under control by psionic manipulation, psychological terror, and regular culling. Not only do these practices keep the brains tastier and healthier, they keep the illithids themselves in better condition, for they will still have to hunt down their own prey.
The 'herd-thinners' are the wilderness specialists of the Tamer Creed. They participate in the management of the 'wild game preserves' by culling the aged, sick, or overly rebellious. They track down and recapture thralls who have escaped from the sunless cities of the illithids. They act as guides for other mind flayers through dangerous wilderness areas. Due to their skill at both tracking prey and subduing it, they are often called upon to capture 'wild thralls' for specific purposes -- research and experimentation, interrogation, or performance-eating, for example. Oddly enough, they may even administer first aid to an injured 'wild thrall' if such an action fits in with the current population management plan for the area. Herd-thinners are the 'big game hunters' and conservationists of illithid society, and are simultaneously admired and perceived as rather odd by their fellows.
While there can be numerous differences between individual herd-thinners, a 'typical' herd-thinner is at least somewhat stronger, more agile, and/or more hardy than others of its kind. They are less likely to have developed their natural psionic abilities beyond the norm for a typical flayer (other than those abilities specific to herd-thinners), and a few flayers with worse-than-average psionic gifts have deliberately chosen this profession. Most herd-thinners were originally rangers, but other combinations (particularly ranger/rogue) also occur. While virtually all of them carry some means to preserve their brains (for eventual inclusion with the Elder Brain of that mind flayer's community), herd-thinners are generally much more willing to take risks than an average illithid.
While the prestige class originated on Gyrus, the herd-thinner's specialized practices have spread into other illithid societies, particularly those that have significant activity outside the Underdark. Herd-thinners associate most closely with other members of the Tamer Creed or the Nourisher and Ariser Creeds.
Hit Die: d8.
Weapon and armor proficiency: As rangers. If the herd-thinner did not have these weapon and armor proficiencies before, it gains them.
Requirements: To qualify to become an illithid herd-thinner, a characer must fulfill the following criteria:
Race: Illithid or illithidkin
Base Attack Bonus: +8
Feats: Track, Endurance
Move Silently: 14 ranks
Hide: 14 ranks
Knowledge (at least one of geography, nature, or dungeoneering): 12 ranks
Survival: 5 ranks
Class skills: The illithid herd-thinner's class skills are:
Climb (Str), Craft (any) (Int), Heal (Wis), Hide (Dex), Intimidate (Cha), Jump (Str), Knowledge (dungeoneering) (Int), Knowledge (geography) (Int), Knowledge (nature) (Int), Listen (Wis), Move Silently (Dex), Search (Int), Sense Motive (Wis), Spot (Wis), Survival (Wis), Swim (Str), Use Rope (Dex)
Skill Points At Each Level: 6+Int modifier.
Class level | BAB | Fort save | Ref save | Will save
1 | +1 | +2 | +2 | +0
2 | +2 | +3 | +3 | +0
3 | +3 | +3 | +3 | +1
4 | +4 | +4 | +4 | +1
5 | +5 | +4 | +4 | +1
6 | +6/+1 | +5 | +5 | +2
7 | +7/+2 | +5 | +5 | +2
8 | +8/+3 | +6 | +6 | +2
9 | +9/+4 | +6 | +6 | +3
10 | +10/+5 | +7 | +7 | +3
Manifester level note: When determining the effective manifester level for the psionic powers specific to the herd-thinner prestige class, combine the herd-thinner's illithid racial levels with its PrC levels. For example, an illithid Ranger 3/Herd-thinner 3 would manifest its baseline illithid abilities as an 8th-level psion, but would manifest its PrC abilities at 11th level.
Class Features:
Subdue the prey: Starting at first level, when dealing nonlethal damage to an enemy using a lethal weapon, a herd-thinner takes a -2 penalty on its attack roll, rather than -4. At third level, this penalty drops to 0. A herd-thinner may even choose to deal nonlethal damage when attacking with its tentacles, though obviously it will refrain from using its Extract ability in this case.
Mark the prey: Illithid herd-thinners are greatly feared for their ability to psionically track their prey over long distances. This ability is in reality a highly specialized form of clairsentience. As a full-round action requiring concentration, a herd-thinner may psionically mark a sentient creature within 100 feet, provided it can locate the target (by sight, telepathy, etc.). Psionic power resistance applies. Powers such as Escape Detection or items such as an Amulet of Protection Against Detection and Location prevent a mark from being established on the intended target.
Once the target is successfully marked, concentration is not required to maintain the mark. This ability penetrates ordinary barriers, but will be blocked by sheets of lead, several feet of stone, etc. The target must be a sentient creature with an intelligence of at least 3, and must fail a Will save of 17 plus one-half the herd-thinner's class level (round down). Once the mark is set, it is permanent unless the herd-thinner chooses to remove it, the prey dies, the herd-thinner dies, or the mark is successfully removed by the 'prey' or a third party. The mark itself is invisible and intangible. A successful Detect Psionics on the victim will reveal the presence of a mark, but not the identity of the illithid who created the mark. Dispel Psionics or a Null Psionics Field will temporarily suppress, but not remove, a mark. Powers such as Escape Detection or items like an Amulet of Protection from Detection and Location will suppress a mark as long as the powers/items remain in effect. Aura Alteration or psychic chirurgery will permanently remove a mark. No more than one individual can be marked by an illithid herd-thinner at a time.
At first level, the herd-thinner can track a marked target anywhere within 50 miles. At 4th level, this range extends to 500 miles. At 7th level, the herd-thinner can track its target anywhere on the same plane.
As a full-round action requiring concentration, the herd-thinner can check the current status of the marked individual. Distance and direction are indicated, as well as whether the 'prey' is awake, asleep, unconscious, injured (i.e. around 100%, 75%, 50%, 25%, close to 0% of its normal HP total), or dying (0 to -9 hp), and whether it is currently subject to any undesirable status effects (diseased, stunned, paralyzed, poisoned, etc.). No more detailed information is available via a mark -- although an illithid with access to the appropriate powers or spells can use the marked individual as a scrying focus!
Sense mark: Starting at first level, an illithid herd-thinner automatically senses the presence (approximate direction and distance) of any individual that is currently marked by the Mark the prey ability, either by the herd-thinner itself or by other herd-thinners, that passes within 100 feet. It does not learn the identity of the mind flayer who placed the mark or any other information by means of this ability. This ability is blocked by those abilities that suppress the mark itself or by lead sheeting/thick stone.
Cloud mind: At 4th level, a herd-thinner gains the ability to use Cloud Mind 3 times per day.
Disorienting strike: At 6th level, once per day, a herd-thinner may declare a disorienting strike while performing either a melee attack with an equipped physical weapon, or a ranged attack with a missile weapon (provided that the target is within 30 feet). If it lands, the target must make a Fortitude save (DC is 17 + one-half of the herd-thinner's class level, rounding down) or take subdual (i.e., nonlethal) damage equal to 20% of its current HP total and be slowed for 1d4+1 rounds (in addition to the damage from the melee/missile attack itself). Half of the subdual damage still occurs on a successful save. This ability is psionic in nature (power resistance applies) and is effective against creatures with an Intelligence score of 3 or more. At 9th level, a herd-thinner is able to perform a disorienting strike 3 times per day, but not more often than once per hour.
Bonus feats: At 2nd level, and every three levels thereafter, a herd-thinner may select a bonus feat from the following list: Greater Two-Weapon Fighting, Improved Multiattack, Improved Natural Attack (tentacles), Improved Precise Shot, Improved Two-Weapon Fighting, Manyshot, Multiattack, Rapid Shot, Two-Weapon Fighting. The herd-thinner does not need to meet the usual requirements for each feat (i.e. Dex 17+ and similar), but must take prerequisite feats from this list first (i.e., the herd-thinner must take Two-Weapon Fighting before taking Improved Two-Weapon Fighting).
Roleplaying notes: A herd-thinner does not like sunlight a bit, but is more practiced at surviving in sunlit environments (if it has to) than an average illithid. Similarly, for dry conditions, a herd-thinner can cope much longer without a dampsuit. Most herd-thinners are 'risk-takers' by illithid standards; while not suicidal, they are less likely to flee from combat.
How many levels is this PrC? 10 I assume? Also - do you have progressions picked out for BaB, Fort, Reflex, and Will?