OSR: Illithids

This is a super-intelligent, man-shaped creature with four tentacles by its mouth which it uses to strike its prey. If a tentacle hits it will then penetrate to the brain, draw it forth, and the monster will devour it. It will take one to four turns for the tentacle to reach the brain, at which time the victim is dead. A Mind Flayer will flee if an encounter is going against it. Their major weapon, however, is the Mind Blast, a wave PSI force with a 6” directional range and a radius of 5’.
-The Strategic Review #1, Spring 1975.
This is the first mention of the Mind Flayer, in its entirety. All the essential elements are present. Magical resistance. Brain-eating. Mind blast. 

Eldritch Wizardy (1976) adds, "They speak only their own arcane language and several other strange tongues purportedly those of terrible races which inhabit regions far beneath the ground."

The AD&D Monster Manual adds, "Mind flayers are found only in subterranean places, as they detest sunlight. They are greatly evil and consider the bulk of humanity (and its kin) as cattle to feed upon."

Everything else - invasions, tadpoles, mastermind brains in tanks - came later. Here's my take on the Mind Flayer, based on the information above and nothing else.


Major Features

-pale purple cave squid. Shimmering skin, rippling with patterns.
-bulbous head with large white eyes and four small tentacles around a hidden beak
-two tentacles used as arms, ending in delicate finger-sucker protrustions
-two tentacles used as legs, ending in flat fins with rippling sides. Can run and also silently glide.
-the tentacles have minds of their own. They are steered like a houndmaster steering his hounds. 
-hyperintelligent carnivores

Horrible cave-squid. They crawled from a sea buried by plate tectonics. Ten thousand feet of rock above. No light, but their ancestors were used to no light. They evolved as the surface evolved, found sentience, tools, magic.

Slithering, every-vigilant, they conquered their environment. They knew nothing of the outside world, of other races, of the surface. Their focus was inwards. Immortality. Mathematics. Science, untroubled by competition.

Yes, they had wars and revolutions in their deep-cave cities, but they always crawled back from extinction sharper and wiser than before. Merciless, perhaps, but not cruel. There are no secrets among the Illithid; they can read each others thoughts in patterns of flashing skin and writhing tentacles. Deception is possible but exhausting and forbidden. In close proximity, their minds are linked, a blind pit of slimy arms and entwined thoughts and souls.

They have souls, but no angels or demons. The are a forgotten race, buried by accident, left to grow unexamined. They have no afterlife. 

The Apocalypse

It wasn't so long ago. An Illithid surgeon tried to save the life of a traveler, a visitor from the upper world. A rarity, but one the Illithids were slowly coming to accept. Their cosmology overturned. First contact.

Some brain fluid was accidentally ingested.

Illithid society collapsed within weeks.

Their biology evolved in isolation. Brain matter from vertebrates, particularly the complexs folded cortical structures found in intelligent creatures, is a drug to them. They crave it instantly and totally. It soothes their minds, smooths away pain, increases concentration, improves them, completes them. It feels wonderful. It is immediately addictive.

Like this. Atlantis crossed with Mad Max.

Fortresses and Factories

In small groups or alone, Illithids are spreading through the Veins. They build fortresses and cities. They create slaves and tools. Sometimes, their plans are ruined by armies or natural disasters. Sometimes, they fall to their greed for brains. Plans splinter and factions dissolve when the supply of brains runs low.

Their technology and magic was hastily re-purposed by the survivors of the first great conquest. There is no time and no real will to create better tools, if the ones at hand satisfy their immediate needs. Their deep cities are abandoned, shattered, stalked by deranged brain-starved Illithid and their wretched servants. Their culture has no heartland. There is only The Front.

Fortresses spring into being overnight, inhabited by a single Illithid or a small group and their newly crafted minions. They capture as many sentient creatures as possible, destroy organized resistance with brutal precision, and slowly expand their control of the area. The Illithid are perfectly content to farm brains... provided their supply isn't interrupted. Farming projects collapse when their leaders seek a quicker fix.

Tom Vernon Field


Illithids rarely rove the Veins alone.

Stats: as giant beetle
An isopod-like creature from the Illithid's underground sea. Poor vision, thick armour, and long flailing front appendages. The Illithids used them as hunting-hawks. They entangle their targets, lock their segmented tentacles, and go dormant. They are almost impossible to remove. Each one occupies 4 Inventory Slots on a successful hit.


An agent of the Illithids. A sack of chameleonic skin with muscles, bones, organs, and false memories inside. Only partially self-aware. Designed to observe and lure.

Hunting Hound
Stats: as a wolf
A low, four-legged creeping creature. Most of its length is its nose, a huge wet fold of flesh and sensors running from the tip of its head to just before the rear legs. Six eyes, wet and staring, arranged in a ring near the snout. A delicate, human mouth buried deep below. No claws. Just rippling skin (to communicate its findings with the Illithid) and a soft, careful step. It's made out of people, but hastily, without elegance.

The Illithid stick them to walls and ceilings. A spinal cord, brainstem, eyes, and ears. Adapted for the dark, kept alive in thin glass tank, linked in vast networks of lobotomized sensors. They see and hear everything but understand nothing. The agony of their existence overwhelms any surface creature trying to tap into the network, but the Illithids are immune.

Stats: as an ogre

A grim, headless stack of muscles. Focused brutality with no real mind. Rubber skin to keep the organs in. Traps weapons in its flesh. No subtlety, but no need for subtlety either.


Pelican-mouthed, filter-gills chopped back. A transport creature, crawling on implanted metal legs, useless fins flapping. Toss in captives.


Not actually squid-people. Improved captives. Heads coated in rubber, bulging strangely, buzzing, throbbing. Stumbling, but still aware. Capable of speech, plans, coordination. Fanatically loyal, but still sentient, still aware of what they were. The control modules are crude. The Illithids only make them if the supply of brains is abundant.

Squidlings with larger head-sacks and more surgery. They speak the local prey languages. They can interpret an Illithid's mood but not its thoughts, so they have to make up demands as they go along. Cripplingly, hideously fearful and eager to please.

Tools and Treasure

A Silver Orb
Caress it, and all fire in a 60' radius turns to black ichor.

A carved piece of stone with a metal handle. Wave it, and walls of impure salt appear. Used to block escape routes. There may be larger versions. Small ones can fill 2d6 10'x10'x1' segments a day. Can also be used to build bridges. The salt can be smashed but it takes time.

Gravity Ring
Iron, the size of an acorn. An arrow inside. The ring feels heavy and turns slowly. Anything touching it, up to 1,000lbs and 30' radius, treats the direction the arrow points as "down".

Memory Bracers
Clip onto the arms with surgical steel clamps. Can be cut free but not removed. Neurons writhe inside. They contain memories of 1. weapon-use and combat, 2. engineering, 3. slave control, 4. navigation, 5. local races and tactics, 6. pain and fear.

Tumor Bandage
A strip of flesh in a glass case. Removes all current Fatal Wounds. Heals 1d6 HP per round attached to a wound. Can heal Injuries, cure Blindness and Deafness, etc, but not restore lost limbs. If overhealed, gain temporary HP up to your original max HP, then Save with a penalty equal to the HP gained. Failure means you have cancer. Symptoms will develop in 1d6 months. Not an issue for slaves. 1d4 uses.

Reception Needle
Matched pair. Stab one just next to the eye of one creature. Stab the other one just next to your eye. There's no pain, just a curious sense of pressure. You can see through the creature's eye; they can see through your eye. Image is sometimes fuzzy or distorted. No range limit. Only works on vertebrates.

Miracle Scalpel
Cuts flesh but instantly seals nerves and blood vessels. Like slicing bologna. Too small to be used as a weapon, and the grip isn't designed for human hands, but it makes difficult surgery much easier. Worth a fortune on the surface. Worth a fortune in the Veins too; it's probably one of the few things that could genuinely interest a Drow.

Knowledge Injectors
A knife-drill-syringe-pistol. Specialized skills, drawn out and liquefied. A crude technology. Injects clusters of new neurons directly into the brain. Memories too. One setting injects a random skill or memory set. The next setting injects hundreds. You know anything you care to name, provided someone else alive and in the Veins could possibly know it, but each time you remember something from the injected memories you must Save. After 10 days or 3 failed Saves you go permanently insane.

Drowning Ray
A small charm or token. 50' range, one target. Must Save or believe they are drowning in a column of dark, cold sea water. Target will start to float slightly. Targets will fall unconscious after Con. bonus minutes. Recharges every 12 hours.

Vehicles and Engines

Illithid Submarine
Like a small nautilus. Can fit - or, more accurately, swallow - 3 people. Controls are touch-sensitive and coat your arms in sticky neuron-implants. No safety lock - the Illithids never needed one before their apocalypse - so you can drive it freely. Can swim upstream and climb waterfalls.

Illithid Chasm-Climber
A sort of mechanical crab. Front edge is a sharp wedge, mirror-bright. Small ones can carry one person. Large ones can carry towers or fortresses. Slips into a crack in the rock and compresses, sliding upwards, folding through space and matter. As long as there is a fissure, even hair-thin, the crab can move. Everyone inside is folded into an unpleasant configuration. Not harmful, but it's very odd to see your own body being spread out on a 2D plane.
Tsvetelin Krastev

Survival Strategies

An Illithid alone, or with a few creatures to assist. Desperate, raving. Exiled from a fortress or the victim of some internal collapse, sabotage, or rescue effort. Laser-focused on acquiring their next fix, twitchy with need and hunger. They can see perfectly well in the dark. They will avoid conflict until an isolated or weak target is available, then strike, devour their brain, and retreat.

Small Farm
An Illithid fortress, like a coral reef made from stone and black oiled metal. Sealed caves, where food poylps grow on nothing but water, limestone, and sulphur, feed a trapped population. The poylps can support an entire ecosystem; the Illithid leave their servants to manage the details. As long as the brains flow, the arrangement is quite stable. Some villages consider the Illithids kind and benevolent protectors, and they are not entirely wrong.

Large Farm
A series of caves, linked and lined with black oiled metal and strangely sculpted stone. Entire caverns full of polyps and dim light. Specialized areas for certain types of brains. Memory extraction facilities. Minds can be seasoned and tuned; eager collaborators present the very finest minds to their Illithid masters. Death-mazes to provoke terror, pleasure gardens for delight, hallucinogenic fungi for a touch of sour strangeness. Ambitious schemes, often on the edge of collapse.


Several linked farms with a common cluster of fortresses in the centre. Brains banked and hoarded. Greater security, but greater paranoia, either of outside threats or other Illithids. An echo of former Illithid society. Great leaps made in technology and understanding the strange creatures of the Veins. New weapons and disciplines created, entire new fields discovered. Ambassadors received, traders and explorers housed and questioned politely.


Internal sabotage, rebellion, hubris, or an interruption in supply cause chaos. The Illithid turn on their supply first, then on each other. They retreat to their fortresses or flee entirely. The city is left a ruined shell full of escaped slaves, deranged experiments, and half-functioning technology. They cycle repeats.

Trade Goods

An Illithid on the run, or one with limited resources, should be treated as a universal threat. Communication is difficult; negotiation is next to impossible. It's kill or be killed. But a well-fed Illithid in a fortress or a city is a different creature entirely. They are more than willing to play the long game. They might not understand the details of an arrangement, but they are more than willing to make one.

Gold and Gems

The Illithids have little use for the trinkets and treasures their captives once prized. They pay well, sometimes too well. They will eagerly accept occultum but never sell it.


The Illithid will sell excess slaves to secure alliances, distract armies, or solve disputes. A well-maintained farm produces a small excess; a city might be able to offer hundreds of custom-build slaves to any bidder. Those who would turn the miltiary slaves of the Illithids against their creators rapidly discover their folly. Nevertheless, they are valuable and utterly obedient.

Excess meat is also sold, mainly to the Ghouls and the Dvergr. Visitors to Illithid cities are well fed.


From the surface, from other parts of the Veins, from anywhere. The stranger the better. Dozens of well-traveled slave traders circle through the Veins. The most beautiful captives go to the Drow. The most learned, experienced, or unusual go to the Illithid. Anything they can't sell elsewhere goes to the Ghouls.

Only vertebrate slaves will do. Antlings are safe from the Illithids predation. They will be exterminated as pests or ignored, as required. Dvergr are inedible. Drow, with their vestigial biology, are unpalatable.


Think of them as spices. You can trade your memories to the Illithids too. If you are a trusted collaborator, they may even give you an extraction rig of your own.

Safe Passage

If you are known to the Illithid they will try not to eat you. Safe passage through their territories is easy. It may need to be negotiated every few miles, but most Illithid see everything in terms of prey or tools. If you prove you are a useful tool, they will ignore you, or possibly even reward you beyond your wildest dreams. 

How Do The Illithids See You?

This is a sense-diagram found in an Ilithid cave. It is unknown if the diagram represents instructions, a code, or a branded logo for a particular variety of slave. 

Side Note: if anyone remembers a science fiction short story where these mysterious aliens turn up and start demanding children or they'll destroy the Earth, and then people slowly realize that the children are being turned into drugs, let me know.


  1. https://en.wikipedia.org/wiki/Torchwood:_Children_of_Earth

    1. That's close, but this would have been 1990 or earlier... I think...

    2. I will see what I can find... 8^)

  2. This is really great. There's a lot of background on the illithid in recent monster manuals and other books, but this is what really gives you a sense of what it would feel like to talk to one, or how they would attack and fight. Loving your rendition of the underdark and all its denizens, you're a master of your craft!