(d20 SRD monster converted to ACKS)
The Aboleths are old, unfathomable creatures, the product of aeons past. They were old when the Serpentmen were young; they might have been old even when this world has formed from a stellar nebula. Where they came from remains a mystery, as the Aboleths themselves are tight-lipped about their ultimate origin. But as each of them is old, their knowledge is enormous. They spend ages in their underwater lairs, brooding, plotting… With endless patience. A single Aboleth, intelligent beyond the Human ability to understand, may be the centrepiece of a massive conspiracy, spun across the centuries towards an end known only to that alien mastermind.
The Aboleth itself is a revolting, green but pink-bellied, fishlike amphibian found primarily in subterranean lakes and rivers, or deep beneath the oceans. Four pulsating blue-black orifices line the bottom of its body and secrete gray slime smelling like rancid grease; it has four long tentacles used for grabbing, whipping and manipulating objects. It uses its tail for propulsion in the water and drags itself along with its tentacles on land. An Aboleth weighs about 6,500 pounds.
An Aboleth in combat utilizes its mind, as well as its watery lair, to its advantage. First, three times a day, it may Enslave a sentient creature; the victim must save vs. spells, or become the Aboleth's mental thrall, fully under the creature's command, as per the Enslave spell. An Enslaved creature obeys the Aboleth’s telepathic commands until freed by Remove Curse, and can attempt a new save vs. spells every 24 hours to break free. The control is also broken if the Aboleth dies or travels more than 1 mile from its slave. An Aboleth also possesses the following mental powers for use at will, as per the spells of these names: ESP, Hypnotic Pattern, Phantasmal Force, Hallucinatory Terrain.
A blow from an Aboleth’s tentacle might cause a terrible affliction. A creature hit by such a tentacle must save vs. polymorph or begin to transform over the next 1d4+1 minutes, the skin gradually becoming a clear, slimy membrane. An afflicted creature must remain moistened with cool, fresh water or take 1d12 points of damage every 10 minutes. The slime reduces the creature’s armour class by 1 (but never to less than 0). A Cure Disease spell cast before the transformation is complete will restore an afflicted creature to normal. Afterward, however, only Restore Life and Limb may cure the affliction.
An Aboleth underwater surrounds itself with a viscous cloud of mucus, roughly 1 foot thick. Any creature coming into contact with and inhaling this substance must save vs. polymorph or lose the ability to breathe air for the next 3 hours. An affected creature suffocates in 2d6 minutes if removed from the water. Renewed contact with the mucus cloud and failing another Fortitude save continues the effect for another 3 hours. This effect may be removed by Cure Disease.
Most Aboleths breed (from captured slaves), Skum - revolting fish-amphibian-men, to serve as their hand, ears and eyes outside their watery lair. These creatures possess a slimy skin, and may breath indefinitely both under and outside of water. While rarely armed with weapons, they possess a powerful bite, as well as sharp claws. Skum lack much organization or willpower of their own, and care little for treasures. Their presence usually signifies the existence of an Aboleth lair in the vicinity.