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Neothelids were extremely rare creatures, so called as they were illithid tadpoles who had undergone neoteny. They typically appeared once a mind flayer society was destroyed and the tadpole tank left unsupervised. The larval illithids engaged in cannibalism until the last survivor became a gargantuan leviathan loathed by all, especially the mind flayers themselves.[1][4]


Neothelids were voracious and destructive, constantly searching for intelligent lifeforms so as to eat their brains. They were ferocious predators driven only by a desire to consume. Their low intelligence made them undetectable even by elder brains.[1]


Neothelids were slime-covered worms with a quadri-tentacled mouth that resembled gigantic versions of illithid tadpoles. They were often mistaken for purple worms due to their purple skin, and massive larval body structure.[4]


Neothelids shared numerous abilities with illithids and elder brains, capable of levitating at will, resisting magical abilities, sensing sentient beings, and possessing blindsight. A neothelid could send the minds of its prey into disarray and use telekinesis to move things around it, although its poor mind meant this was taxing for it. It was also capable of breaking the minds of its victims and dissolving their bodies using its acid-like[1] enzyme-based breath weapon that dissolved most organic tissue, leaving only clothing, possessions, and brain intact. The latter of which is then used for sustenance.[5]

Neothelids could use their mouth tentacles to squeeze and draw in prey, swallowing them whole and digesting them from inside their stomachs. If hurt too much from the inside, they would have to resist the urge to regurgitate their prey, and those who survived being consumed could crawl out their carcasses.[1]


To create a neothelid, not only must an illithid tadpole not undergo ceremorphosis, but the elder brain of the colony must be absent, as the elder brain would normally eat all tadpoles that failed to undergo ceremorphosis. Without the elder brain, the tadpoles would be forced to engage in cannibalism in order to survive. If one tadpole survived the resulting chaos, it would grow to the size of a dog, forced to flee its home and feast on rats and other vermin until it grew larger.[4][6] Without the ability to create tunnels of their own, they relied on preexisting tunnel systems to travel, eventually relying on purple worm tunnels to travel in. The process of becoming a neothelid completed when it digested a sentient mind. Doing so caused a similar reaction to that caused by the consuming the host's brain during ceremorphosis, granting the neothelid self-awareness and psionic powers. They constantly hunted for new brains, dissolving their victims' bodies with acid breath and devouring the untouched brains.[6][1]


Mind flayers saw neothelids as abominations and never normally created one willingly, since allowing one to exist was one of the largest taboos in their culture. Likewise, a neothelid had no knowledge of its link to the mind flayers and would gladly consume them the same as any other sapient being.[1]


One of these creatures took up residence in the old illithid colony of Phanlinksal.[4]

In the late 15th century DR, the ulitharid Extremiton and its colony in the Seadeeps deliberately bred a neothelid with the purpose of unleashing it upon the githyanki contingent in the Crystal Labyrinth of Undermountain.[7]



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