Aboleth

Picture a bloated, finned eel the length of a riverboat. Its hide is a mottled blue-green flecked with gray, fading to a pinkish belly that hides a soft, toothless mouth. Three narrow red-violet eyes sit stacked one above another behind ridges of bone, and four whip-like tentacles, each about ten feet long, sprout from the front of its head. Along its underside, four throbbing vents leak a gray slime with the reek of spoiled cooking fat. In water it drives itself forward with its broad tail; on land it hauls its bulk along with its tentacles.

Each of the aboleth's four tentacles deals 1d6 damage. Anyone struck must save vs. spell or watch their skin turn into a clear, slick membrane over the next 1d4+1 rounds. From then on the victim must keep that membrane wet with cool water or lose 1d12 hit points every turn it dries. A cure disease cast before the change finishes halts it; once the membrane is complete, only cure serious wounds restores normal skin.

Because it is slow out of the water, the aboleth prefers to let prey come to it. It can conjure convincing illusions at will, complete with sound, smell and other sensations, to bait victims within reach.

Three times per day it may try to enslave one creature within 30 feet. A failed save vs. spell leaves the target obeying the aboleth's telepathic orders, though a thrall will not fight on its behalf. The hold breaks with remove curse, dispel magic or the aboleth's death. A thrall carried more than a mile away also earns a fresh save once per day.

Underwater, the aboleth wraps itself in a foot-thick cloud of mucus. A creature that inhales it must save vs. poison. On a failure its lungs can no longer handle air; instead it breathes water as if under water breathing for 1d3 hours, and each new contact with the cloud extends the change. An affected creature that tries to breathe air chokes to death in 2d6 rounds. Wine or soap washes the mucus away.

Aboleth live in small broods: one parent and up to three grown young who are every bit as large and strong, yet obey the parent without question. Each aboleth carries both sexes. About once every five years a mature adult withdraws to a hidden grotto, lays a single slime-coated egg and guards it for the five years the embryo needs. The newborn then takes roughly a decade to reach full size.

Their lives revolve around gathering thralls, humans above all. Tales speak of sunken cities built by enslaved hands and of secrets older than humanity, but no one has proven either. What is certain is that an aboleth's memory is vast: a hatchling is born knowing everything its parent knows, and an adult absorbs the knowledge of any thinking creature it eats. Its treasure is whatever its thralls once owned, buried in the cave floor under a layer of gray, foul-smelling slime.

An aboleth will eat nearly any organic matter, grazing on algae and tiny water life, but it favors intelligent prey because a single meal feeds both body and mind. Even the largest sea creatures steer clear of it, so it has no natural enemies. Alchemists prize its slime as an ingredient for potions of water breathing.