The Neh-thalggu, or Brain Collectors, are an aberration originating from the Dungeons & Dragons setting of Mystara. Hailing from the Dimension of Nightmares, and later the Far Realm, where they are figures of dread and awe to the diabolus race in much the same way that dragons are to humans, a neh-thalggu is a grotesque monster, somewhere between a crab and a spider, with a toothy maw, myriad tentacles, and bulging blisters that they use to house human brains. Unlike the common illithid, neh-thalggu don't merely eat brains; rather, they are able to enhance their own mental prowess by storing stolen brains - the more brains stashed in their preservative blister-wombs, the more powerful they are.
First appearing in the Basic D&D adventure module X2: Castle Amber, neh-thalggu then got an entry in the Creature Catalogue. They were subsequently updated to Advanced Dungeons & Dragons in the Mystara Monstrous Compendium Appendix. In 3rd edition, they appeared as epic tier monsters in the Epic Level Handbook, and as a more reasonable CR 7 creature in issue #144 of Dungeon Magazine, officially representing the "larval stage" of the epic version. Despite this, such is their obscurity that Pathfinder managed to use them in their Golarion setting, slipping them into their 2nd Pathfinder Bestiary splatbook, whilst the Iron Gods adventure path would present its "mature" form, the Yah-thelgaad in part 4: Valley of the Brain Collectors.
Brain collectors (Neh-thalggu in their own language) are rare creatures who occasionally cross the barriers separating their distant home from the Prime Material Plane. Only near sources of great magical energy, where the fabric of time and space is twisted, can they find small gateways to Mystara, where they collect the brains of intelligent beings.
Each specimen of this hideous race has a yellow-orange body – bloated, oily, and amorphous – with dozens of short, writhing tentacles. Six crablike legs allow it to scuttle about. Four large, yellow, bulging eyes and a tooth-filled maw are set in its bulbous head. The head may also have a number of distinctive lumps (up to twelve), each one housing the brain of another intelligent creature.
Neh-thalggu do not think like any other creature. They speak their own tongue and that of diaboli. They can also speak and comprehend the languages known by any creatures whose brains they’ve swallowed.
The brain collector’s method of attack is a powerful bite with its razor-toothed jaws, inflicting 1d10 points of damage with each bite that hits.
Each brain collector can cast spells, depending on how many brains it has collected. Roll 1d12 to determine how many transplanted brains the monster already has in its head. Each transplanted brain can hold a single wizard spell, no bigger than 3rd level (these can be chosen by the DM or randomly determined by dice roll; 1d3 for level and then according to wizard spell lists).
A brain collector can attack with its bite or with a single spell in a given round. Although the nature of its intelligence is unfathomable, brain collectors display a considerable tactical cunning in combat; they will use their available spells to the best possible effect.
A brain collector takes great care as it fights, to avoid doing damage to the cranium of its opponent. As its name suggests, the brains of sapient foes are very precious, indeed.
Though brain collectors have a completely alien psychology, “chaotic neutral” is the alignment that best describes them. The Neh-thalggu do not have hostile intentions as such; rather, they do not seem to regard humans or or other humanoids as people.
Brain collectors are known to exist on the Demiplane of Nightmares, where they hold a mythic position in the folklore of diaboli, like that of dragons in human tales. Diaboli regard Neh-thalggu as creatures of power, cunning, and inscrutability, and brain collector magic can affect diaboli.
While Neh-thalggu exist on the Demiplane of Nightmares and the Prime Material Plane, sages agree the creatures are native to neither. Brain collectors may also be found wandering other known planes, particularly the Astral or Ethereal Plane. On the Prime Material Plane, a brain collector prefers ruins and caverns and other places with little light and infrequent disturbances.
When a brain collector reaches the Prime Material Plane, it immediately begins acquiring as many brains as it can, as quickly as possible. Each collector can store up to 12 brains at any one time. When these creatures slay humans, demihumans, or humanoids, they carefully cut away the top of the head with surgical tools to expose the brain, and then swallow it. The swallowed brain then moves into one of several pockets witbin the brain collector’s own head, forming a distinctive lump. For each brain collected, the creature gains the ability to cast one wizard spell of 1st to 3rd level once per day.
When a Neh-thalggu has collected its 12 brains, it immediately seeks to retum to its home plane. One theory holds that with 12 collected brains, these monsters can, in certain locations, re-open the link to their native world. Fortunately, few 12-brain Neh-thalggu have been encountered; since they can collect no more brains, they are more eager to move along than to engage opponents.
The brain collector may be related in some fashion to the feyr.
Brain collectors have no interest in treasure of any kind; denizens of the Prime Material Plane are curious objects for dispassionate study and ruthless exploitation – cattle, in the brain collectors’ eyes.
Neh-thalggu are predators of the highest order, but they exert little influence on the Mystaran environment.
Far Realm Neh-thalggu
Brain collectors encroach upon the Material Plane from the inconceivable Far Realm in what is actually their larval stage. Terrible beings of unspeakable and unwholesome desires, these monsters are driven to ollect brains and use the knowledge locked within these organs to further their own transformation into beings of godlike power (Epic Level Handbook 207). Uncaring of the empty husks cast aside by their feeding, these alien predators use their fleshy meals to generate great bursts of arcane energy. While even the weakest are capable of devouring the sentience from whole regions, a fully ascended neh-thallggu rivals even the eldest dragons and some demon lords in ferocity and arcane might.
Epic Level Handbook Version
Bizarre creatures best known for their unpleasant habit of harvesting humanoid brains, whatever the wishes of their current owners, neh-thalggu endlessly prowl for additions to their collections.
Brain collectors have bloated, yellow-orange, oily bodies that spout dozens of short, writhing tentacles. Ten slightly longer tentacles frame its lamprey mouth, which is filled with row after row of jagged red teeth. Above the gaping maw are four large, yellow, red-irised, bulging eyes, behind which cluster a number of squirming bulges about a foot across. These bulges house the human or humanoid brains the brain collector has harvested to date (up to thirteen brains at a time), which it uses to power its own special abilities. It must discard one of its currently “banked” brains in order to replace it with another. The creatures move with surprising agility on twelve segmented crablike legs (larger specimens have eighteen or even twenty-four legs, juveniles but six). Brain collectors lack fixed internal anatomies and can rearrange organ functions at will, making them very difficult to kill.
Brain collectors hail from a distant reality known to sages only as the Far Realm or Nightmare Dimension. Occasionally juveniles (Large, 10 HD, AC 20) are encountered in isolated locations, but fully grown specimens such as the one described here are quite rare. Both types visit mundane realms in order to harvest the brains they need to fully access their abilities. A juvenile will seize any brains of characters 5th level and higher as opportunity arises, but an adult absorbs only the brains of arcane spellcasters of at least 15th level, passing along rejects to its less fussy mind flayer retainers. A creature whose brain has been harvested by a brain collector cannot be raised, reincarnated, or resurrected while the brain is in the creature, because the collector preserves and draws upon the soul and basic personality of the creature for as long as it retains the brain. A brain collector might be bargained with for the return of a specific brain, but only in exchange for a better (higher-level) specimen.
Brain collectors typically attract a retinue of 1d4+1 mind flayers, drawn by the desire to study the aberration’s technique in extracting brains with ranged attacks and its ability to access the arcane brainpower of the assimilated brains. Some sages have ascribed the illithids’ attraction to simple self-interest (the illithids get to claim the rejects that do not meet the neh-thalggu’s demanding specifications), others to an affinity almost amounting to worship. On rare occasions a neh-thalggu is accompanied by a single paragon mind flayer sworn to its service.
Neh-thalggus’ own language is a silent sign language “spoken” with their writhing head-tentacles. They can also communicate telepathically with any creature that has a language within 100 feet.
Neh-thalggus are aliens from distant worlds, traveling the gulfs of space on immense living ships that swiftly decay when they land upon a new world, leaving behind a deadly cargo of hungry monsters. Neh-thalggus are carnivores, but they do not digest humanoid brains they eat—rather, these brains lodge in one of several bulbous blisters on the Creature’s back and help to increase its intellect.
Some speculate that neh-thalggus encountered in this reality may merely be juveniles of their kind, perhaps exiled from their home worlds by greater kin until they can prove their worth on other worlds. Their brain collections may be a morbid form of currency in their home realm, or the thoughts in these brains may merely be fuel for a dark apotheosis into an even more sinister mature form.
When a neh-thalggu has absorbed a critical mass of thoughts and memories from an unknown number of humanoid brains, its body undergoes a horrific transformation. The creature enters a state of torpor, its body curling into a tight ball as it consumes the oldest of its seven stored brains to trigger the metamorphosis. Over the course of several days of self-consumption, the neh-thalggu bursts from the shell of its old body into its new incarnation as a yah-thelgaad.
While the yah-thelgaad shares many of the features of its less powerful progenitor, it is in every way a more powerful creature than it was before. While the capacity to store one fewer brain than a neh-thalggu presents some disadvantage, the yah-thelgaad gains twice as much power from a collected brain as its lesser kin does. In addition, these creatures need not limit their harvest to the brains of humanoids - any Small or Medium creature's brain will do.
Yah-thelgaads are zealous devoted to the inscrutable causes of the Dominion of the Black, but they are also notoriously devout believers in that alliance's weird theology, worshipping a concept they refer to as the "Ineffable Void", among other cryptic mysteries. It is not uncommon for yah-thelgaads of high rank to also possess inquisitor or oracle levels, lording their authority and fanatical faith over those in their charge - the most powerful yah-thelgaads often take levels in mystic theurge to combine their class-based mastery of the divine with their stolen brains' arcane lore.
Yah-thelgaads often supervise the Dominion of the Black's surgical and genetic engineers on major projects, pushing those agents to attempt greater and more horrific procedures. For all their legendary cruelty, however, yah-thelgaads don't appear to gain pleasure from such experiments. Indeed, they don't seem to feel any emotions at all on their own, but rather experience such sensations vicariously through the memories of the brains they've collected. In this way, the creatures know lust, fear, hatred and pride without exposing their own minds to the disadvantages of being susceptible to mind-affecting effects.