Much like other aberrant creatures, the anatomy of a grell was truly bizarre. While some held that these flying, tentacled "brains" were the horrific creation of a parallel world or alternate plane, they actually originated from the Far Realm, where the laws of nature differed wildly from those of the Prime Material Plane.
The wrinkled hide of a grell varied from a pale pink-gray to a faint purple-pink in coloration (with older specimens being darker in color than younger ones) which, combined with its damp skin that gleamed wetly in poor light, made adventurers mistake the creatures for disembodied brains. This skin was actually surprisingly leathery and tough; measuring several inches thick on the upper body of a grell.
The only other external features of a grell were its ten strong, rubbery tentacles and its hard beak. The tentacles were each 5-8 feet long (with larger grell having longer tentacles) and made up of hundreds of ring-shaped muscles sheathed in an almost fibrous hide much thinner than the epidermis of the creature's body. Each tentacle was capable of regeneration, and the skin on each featured sharp, hard barbs every 2–3 inches all the way down to almost the very tip. These barbs were hollow, allowing the grell to inject a paralytic venom into its prey, but could also be partially retracted to allow the grell to manipulate objects it didn't wish to pierce or tear. The barbs were made of a bony substance that bore more of a resemblance to the calcified shells that some molluscs secreted than true bone, as it lacked marrow or blood vessels. The beak of a grell was made of the same substance.
Grell internal anatomy was perhaps equally unusual and alien. The creature maintained its internal structure via a soft and flexible cartilage cagework; a grell could compress its body to roughly half of its original height or width with ease, thus allowing it to easily squeeze through surprisingly small spaces. However, they didn't like to do so if they could avoid it.
The brain of a grell was located near the front of the body, above the beak, and was a rumpled membrane that called to mind a crumpled piece of paper. At the top anterior portion of a grell's body, above the brain, was a tangled mass of ganglia that acted as the center of the electroreceptive sense that allowed the eyeless creatures to detect their environment. Behind the brain, at the top center, were a grell's lungs, but a grell's vascular system lacked a heart. Instead it used ten powerful vascular chambers at the base of each tentacle that constricted and retracted together to circulate the aberration's green, copper-based blood.
A grell's stomach was located near the center of the body, with the digestive tract filling the posterior third of the body. Grell fed infrequently and preferred large meals with long intervals between each instance; a 150 lb (68 kg) human was a perfectly manageable food item for an adult grell, and could sustain it for up to three months. However, a grell would have to be practically gorged to turn down a meal, as they would eat opportunistically, even if not very hungry.
After its strange appearance, perhaps the most noticeable thing about grell was their complete lack of eyes, or indeed sight of any kind. However, they possessed two other keen senses that made up for their lack of vision, and these combined granted a grell blindsight. The first was their entire epidermis, which acted as a single "ear", giving them excellent hearing. The other sense was far more mysterious, and was described as a sort of electroreception; a grell was able to sense the faint electrical stimuli produced by both living creatures and inanimate objects within 60 ft (18.3 m) of itself. This sense was startlingly accurate despite its relatively short range, as a grell was easily able to distinguish between two beings of different sizes, a living and a dead creature, and even tell that two boulders had different compositions. It also allowed grell to "see" even in areas of magical silence.
However, this is not to say that such a sense did not have its limitations; a grell would struggle to distinguish between, for example, two humans of a similar size unless they both spoke (a grell's keen hearing would allow it to identify individuals by voice alone). For a grell, such a scenario would be unlikely to be a problem, as non-grell were generally viewed as nothing more than potential prey.
Grell had two priorities: colonize new lands and feed. Although instinct alone drove grell to reproduce, feed, and expand their territory, their intelligence allowed them to plan their actions far better than any pack of wild predatory animals could. Grell fell somewhere between the genius mind flayers and the crazed carrion crawlers on the scale of aberrant creature intelligence, with an intellect roughly on-par with that of humans, albeit modified by their strange alien motivations. As a race, grell were insular and reclusive, and wouldn't live with other creatures. A grell might join a fight alongside non-grell if it led to an easier meal, but would quickly disappear with its prize back to its nest or colony.
Grell originated from the Far Realm, but then colonized the Underdark of every plane. With their hatred of sunlight, the enormous caverns of that unlit subterranean world held great appeal to them, as it allowed plenty of space for them to hunt, build colonies, and practice their strange alchemy. However, it was in the Shadowdark that they were especially plentiful and where the most ancient grell resided.
The average grell had no interest in infiltrating societies, manipulating events on the surface world, or amassing slaves; other creatures, including humanoids, were viewed as nothing more than fresh meat to a grell, and they would consume even the largest and most dangerous of subterranean denizens, although they would not attempt to attack anything stronger than themselves. Grell hunted their prey through the underground corridors of their dark homes, using their ability to navigate without sight to easily outmaneuver their light-relying victims, and shunning the surface world where their natural advantages were useless. The larger and older a grell was, the larger the prey items it would attempt to hunt. After ambushing its victim and subduing it with its paralysis-causing tentacles, the grell would crack open its prey's skull with its beak to remove the brain (which were poisonous to grells), then devour the rest of the body, bones and all. Removed brains were normally discarded, but a grell colony might save them if they knew of any nearby mind flayers.
Generally speaking, grell could be divided into two types: those that lived together in colonies, and those that were feral and solitary. However, there was no animosity between the two groups; both considered the other's lifestyle a matter of personal taste. Grell did not worship any deities, but would show deference towards "great devourers" such as the tarrasque and the "Chained God" Tharizdun.
Those grell that followed their alien motivations to live and hunt like animals were feral and solitary. They deliberately lived away from civilization, instead making their lairs in damp caves near roadways where they could pick off anyone unfortunate enough to either be wandering nearby at night, or that ventured into the grell's cave in search of water. Feral grell were still intelligent however, and would move on before travelers begin avoiding the "haunted" road.
Grell colonies were found only in the Underdark, and typically numbered between four and twelve individuals, but could reach as high as fifty. This was not including any humanoid livestock kept to make feeding easier. Such unfortunates never survived for long, except for the few who treacherously led other humanoids into the clutches of the grell.
Grell society was divided into "soldier", "philosopher", and "patriarch" castes according to age and knowledge. Most grell fell within the soldier caste, and few colonies contained the powerful elder patriarchs, but it was the grell philosophers, with their magical experiments and knowledge of the Far Realm, that truly stood out from their fellow colonists. Although a grell would defer to a higher-caste member, any major decision was voted upon by all adult members of the colony. If a colony decided to pursue an agenda (a rare occasion), it would have been at the prodding of the colony's philosophers.
Grell alchemy was a particular sort of magic practiced by grell philosophers, with other aberrant creatures being the only others capable of using this strange power. Neither truly spell nor alchemical formula and indescribable with words, the best approximation would have been an odd combination of arcane magic, alchemical formulas, and natural science, all adhering to the "laws" that "governed" the Far Realm.
When a philosopher wished to invoke grell alchemy, it first coated parts of its body in alchemical powders and lotion, then motioned with its tentacles while uttering a sequence of screeching, chittering sounds. The effects produced were normally (if such a word can be used to describe anything involved with the Far Realm) subtle; the mind of a foe could become clouded, the surrounding environment could become distorted, or a streak of lightning that created a blinding flash where it struck could be produced. The last example was one of the first experiments a grell completed when it became a philosopher; serving both as a sign of its station and a means of defending itself.
In early Eleint of the Year of Lightning Storms, 1374 DR, a grell in the Vast Swamp joined a group of Shadowscale lizardfolk to attack the Sharptooths at their encampment. The grell hid in the fog, then descended rapidly to paralyze and incapacitate the Sharptooth chieftain Kessessek. However, adventurers parleying with Kessessek ultimately prevailed.
- Cormyr: The Tearing of the Weave • Waterdeep: Dungeon of the Mad Mage
- Finder's Bane • Venom in Her Veins
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