- First Appearance: 03 Strange Bedfellows
- Mentioned by name in 05: The Trick About Falling (3:04:48)
- Armor Class 17
- Challenge Rating 10
- Three Legendary Actions per round
- Lair actions, Regional effects
- Darkvision 120 ft, Passive 20
- Speed 10 ft, 40 ft swimming
- Average/Max HP: 135, 216
Aboleths are bad news. Although their primary domain and advantage is in large bodies of water inside caves deep underground, aboleths are amphibious and can chase prey onto land (though if dropped into their fish tank, they’ll enjoy the occasional troll, ogre, and duergar as a snack). Despite their hideous, fish-like appearance, they are actually diabolically intelligent.
Aboleths never permanently die; their spirits return to the Elemental Plane of Water where their bodies reform. Rumored to be older than the gods, they remember everything over their eons of existence. They spend their time plotting to overthrow the gods once again, who they blame for freeing their mind-controlled slaves and upsetting their hold over the mortal realm.
In combat, the aboleth can charm a creature within 30 feet of it with Enslave, up to three per day. This charm lasts for 24 hours, forces the creature to share its greatest desires with the aberration, allows the aboleth to telepathically communicate with and control the being, and allows the aboleth to psychically drain 3d6 from it, all so long as they both are on the same plane. The victim can make a save once every 24 hours, when it is more than a mile away from the aboleth, or if it takes damage (from anyone or anything).
Any creature that makes contact with the aboleth must make a DC 14 Con save or be forced to breathe only water for 1d4 hours. It also multiattacks with tentacles; a successful hit of one requires a DC 14 Con Save lest the victim be forced to stay in water or take 1d12 acid damage every ten minutes (and be unable to heal outside of water). If treated within the first minute, any spell that cures disease will suffice. After the disease takes effect, only a 6th level healing spell or greater can overcome it.
These are also ignoring the lair and regional effects of the aboleth, including fouled water and enhanced psychic range and abilities. Add the fact that the battle takes place entirely underwater, and the creature becomes a significant threat. Clarota said it well: “The aboleth is dangerous.”