I originally posted this on the Behind the Scenes board. It's not Planescape-specific content, but it's not unreasonable that a couple of these devices could have made their way to the planes (courtesy of the Possessor Creed or other traveling natives of Gyrus).
Thrall prod:
Knowing that while most thralls are easily kept in check by a mind blast to the face, some are more resistant than others, the mind flayers of Gyrus have been using thrall prods for a very long time. In its most common everyday use, a mind flayer might use it as part of a reward/punishment system to break in new thralls, or to punish a thrall for making a mistake or for disobedience. Rarely, it can even be used as a fallback weapon, in case a mind flayer encounters trouble that mind blasts and violent brain extraction can't cure.
The most commonplace variety of thrall prod is a metallic, hand-held rod with controls that allow the wielder to select a power setting. Even being lightly touched by the business end of these weapons results in 1d2, 1d4, or 1d8 points of subdual damage. (This damage is electrical and psionic in character with regards to damage reduction and power resistance. Assuming the recipient is in a condition to be able to resist, the electrical attack is against the defender's touch AC.) A Fortitude save (DC 16) halves the subdual damage. Additionally, on the 1d8 setting, the defender must make a DC 16 Fortitude save or be dazed for 1-2 rounds. The controls allow a mind flayer to change the prod's power setting as a move-equivalent action (though a wielder with the Quick Draw feat may do so as a free action). In addition to the game-mechanics side of things, being on the wrong end of a thrall prod is definitely painful and unpleasant.
The majority of mind flayers believe that long-term or excessive use of these devices does nothing good for the tastiness or overall health of thrall brains (which are not well designed for having electricity course through them). Accordingly, they prefer not to use them at all on thralls who are intended either for performance-eating or ceremorphosis, and usually hold back from using the strongest setting unless it's genuinely needed (especially strong-willed captives or rebellious slaves, for example). Of course, there are also a few flayers who don't mind electrically-fried brains as an interesting taste sensation.
In a pinch, the thrall prod makes a passable club (1d4, lethal damage, plus the subdual damage).
While the most common variety of thrall prod does not have a lethal setting, such prods do exist, most often in the hands of the Tamer Creed. A 'quarterstaff' version exists (1d4/1d6/1d8 subdual or 1d8 lethal settings, daze effect applies to the 1d6 and 1d8 settings). If the user wields it as a melee weapon, it does 1d6 physical damage in addition to the electrical damage. The 'polearm' version is almost purely for military use and is generally used to put down serious thrall rebellions, deal with gith incursions, or deal with foes that a mind flayer doesn't want to go anywhere close to with its tentacles, though they are sometimes used to herd very dangerous creatures from one location to another. These weapons deal 1d8 subdual/1d8 lethal electrical damage (plus chance to daze), plus 1d10 physical damage when wielded as a melee weapon, and have a 10-foot reach.
The 'standard model' thrall prod has 100 charges when created, but the highest power setting consumes 2 charges per use. The 'quarterstaff' model has 50 charges, but the 1d8 subdual and lethal settings each consume 2 charges per use. The 'polearm' model consumes 2 charges per use on any setting, and has 50 charges. Given time and resources, they can be recharged by mind flayer specialists familiar with the inner workings of the weapon (Craft Psionic Weapons and Armor feat, and possibly also knowledge of psionic powers of the energy-manipulation type). A casual glance at the weapon won't reveal its number of charges remaining, but anyone with appropriate fine hand tools and an understanding of qualith script can open the outside casing and calculate the current number of charges remaining from a meter located inside the case.
The daze effect does not stack with itself (i.e. if a thrall prod lands several times in one round, or if a thrall is struck with multiple prods at once), nor does it stack with the stun effect of a mind blast. Use the effect with the longest duration, with 'stunned' as the priority. (If a human is mind blasted for 3 rounds, then dazed with a thrall prod for 2 rounds in round 3, the human's status would be stunned-stunned-stunned-dazed, for 4 rounds of negative status effects, not 5.)
Thrall prods do not confer any attack or damage bonuses, but for purposes of overcoming DR, the standard thrall prod is treated as a +1 weapon. The 'quarterstaff' version is treated as +2, while the 'polearm' is treated as +3.
It's worth noting that, due to their considerable power resistance, the effects of a thrall prod will rarely work against a mind flayer. Additionally, it would be considered the height of insult if a mind flayer were to use this weapon against another of its kind. The 'quarterstaff' version, and especially the 'polearm' version, are normally 'locked' and must be psionically hailed by a psi-aware being before they can be used.
Ineluctable arrows:
Designed specifically to counter githyanki marksmen and spellcasters, these rare arrows (or occasionally bolts) came about through a combined effort by the Creative and Tamer Creeds. A target struck by one of these arrows must save or be affected by the dimensional anchor power (8th manifester level). Additionally, if the dimensional anchor manifestation is successful, the target's power resistance is reduced by 5 for 1d4+1 rounds. (The power resistance reduction does not stack if the target is struck by multiple arrows.)
While they provide no attack or damage bonuses, these arrows are treated as +2 arrows for purposes of overcoming DR. After the arrow has struck a target once, it loses its psionic power and cannot be reused. These weapons are rarely found outside the possession of illithid Tamers or Creative Creed laboratories. They are usually found in bundles of 4, 8, or (rarely) 12.
Other ineluctable weapons:
Very rarely, illithids forge melee weapons (often, but not always, longswords) with the ineluctable property. Up to three times per day, on a successful strike, the wielder can attempt to subject the target to the dimensional anchor power. The manifester level, save DC, and effective "pluses" for purposes of overcoming DR vary by the individual weapon. (Note that melee weapons with the ineluctable property do not reduce the target's psionic power resistance. Rather, they ignore 5 of the target's total power resistance when attempting to dimensionally anchor the target.)
The few ineluctable melee weapons that exist are individually handcrafted by Creative Creed specialists, and are usually the prized possessions of renowned gith slayers among the Tamers. Not only must they be psionically hailed in order for their psionic properties to be used, each weapon requires a specific, predesignated command thought to activate. There is a tendency among illithid Tamers to make the command thought something extremely distasteful or disgusting to githyanki.
Illithids who wish to craft ineluctable weapons of any kind must possess the Craft Psionic Arms and Armor and Power Penetration feats and must be able to manifest the dimensional anchor power. Specialized equipment, rare raw materials, and hard-to-find knowledge may be required, as well.
BoGr Guide to Missile Combat:
1) Equip a bow or crossbow.
2) Roll a natural 1 on d20.
3) ?????
4) Profit!