AC 17 (natural armor)
HP 171 (18d10 + 72; bloodied 85)
Speed 10 ft., swim 40 ft.
Proficiency +4; Maneuver DC 17
Saving Throws Dex +5, Con +8, Int +9, Wis +9
Skills Deception +8, History +9, Stealth +5
Senses blindsight 30 ft., darkvision 120 ft., passive Perception 15
Languages Deep Speech, telepathy 120 ft.
Amphibious. The aboleth can breathe air and water.
Innate Spellcasting. The aboleth’s spellcasting ability is Charisma (spell save DC 16). It can innately cast the following spells, requiring no components:
3/day each: detect thoughts (range 120 ft.), major image , project image (range 1 mile)
Legendary Resistance (3/Day). When the aboleth fails a saving throw , it can choose to succeed instead. When it does so, one of its eyes flashes with green light and then turns dull black. Once all 3 of its eyes are black, it is blind beyond the range of its blindsight until it finishes a long rest.
ACTIONS
Multiattack. The aboleth attacks three times with its tentacle.
Tentacle. Melee Weapon Attack: +9 to hit, reach 15 ft., one target. Hit: 19 (4d6 + 5) bludgeoning damage. The aboleth can choose instead to deal 0 damage. If the target is a creature, it makes a DC 16 Constitution saving throw . On a failure, it contracts a disease called the Sea Change. On a success, it is immune to this disease for 24 hours. While affected by this disease, the target has disadvantage on Wisdom saving throws. After 1 hour, the target grows gills, it can breathe water, its skin becomes slimy, and it begins to suffocate if it goes 12 hours without being immersed in water for at least 1 hour. This disease can be removed with a disease-removing spell cast with at least a 4th-level spell slot, and it ends 24 hours after the aboleth dies.
Slimy Cloud (1/Day, While Bloodied). While underwater, the aboleth exudes a cloud of inky slime in a 30-foot-radius sphere. Each non-aboleth creature in the area when the cloud appears makes a DC 16 Constitution saving throw . On a failure, it takes 44 (8d10) poison damage and is poisoned for 1 minute. The slime extends around corners, and the area is heavily obscured for 1 minute or until a strong current dissipates the cloud.
LEGENDARY ACTIONS
The aboleth can take 2 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. It regains spent legendary actions at the start of its turn.
Move. The aboleth moves up to its swim speed without provoking opportunity attacks .
Telepathic Summon. One creature within 90 feet makes a DC 16 Wisdom saving throw . On a failure, it must use its reaction, if available, to move up to its speed toward the aboleth by the most direct route that avoids hazards, not avoiding opportunity attacks. This is a magical charm effect.
Baleful Charm (Costs 2 Actions). The aboleth targets one creature within 60 feet that has contracted Sea Change. The target makes a DC 16 Wisdom saving throw . On a failure, it is magically charmed by the aboleth until the aboleth dies. The target can repeat this saving throw every 24 hours and when it takes damage from the aboleth or the aboleth’s allies. While charmed in this way, the target can communicate telepathically with the aboleth over any distance and it follows the aboleth’s orders.
Soul Drain (Costs 2 Actions). One creature charmed by the aboleth takes 22 (4d10) psychic damage, and the aboleth regains hit points equal to the damage dealt.
Combat
The aboleth strikes as many enemies as possible with its tentacles in order to infect them with the Sea Change, and then uses Baleful Charm on the biggest threats. When hurt, it uses Slimy Cloud and escapes through a hidden exit. Its thralls sacrifice themselves to cover its retreat.
Legends and Lore
With an Arcana or History check, characters can learn the following:
DC 10 Aboleths are underwater monsters. They are said to have dealings with merfolk and sea hags .
DC 15 Aboleths are ancient aberrations that turn victims into charmed servants.
DC 20 Aboleths maintain a network of spies working behind the scenes in settled lands.
Aboleths are hyper-intelligent amphibians that lurk in underwater caves and strange ruined cities, guarding ancient secrets and sending forth charmed thralls to advance their intricate schemes.
Ancient Empires. Aboleths claim they once ruled barren land and slimy sea alike before the coming of the gods. They commanded legions of fish folk in underwater cities of black stone columns, twisted towers, and floating portals glowing with unearthly light. The ruins of these sunless cities still beckon and annihilate unwise explorers.
Memory Eaters. Aboleths remember their former days of dominion perfectly. Each aboleth gains the memory of any creature it eats, and aboleths consume their elders as well as other prey. Every aboleth is a repository of ancient knowledge, which it will share for a price. If a supplicant asks a sea witch for a service or secret that she can’t provide, she will turn to an aboleth for help.
Well-Laid Plans. Aboleths plot to overthrow the gods, sink continents, and bring about an endless watery empire. To that end, they scheme endlessly to enthrall mighty mortals, acquire artifacts, gain the keys to the krakens’ freedom, and sow dissent and distrust among the gods and their servants.
Every setback can be turned to advantage in time, and aboleths—with their generation-spanning memories—have eons at their disposal. Nevertheless, aboleths always seek to avenge a wrong. Even a slain aboleth can be a dangerous foe; the aboleth that consumes it will inherit its resentments.
1 Tries to detect thoughts , then communicates with you telepathically and offers you a trade: information about something you desire in exchange for a future service
2 Uses major image to create an illusion of something you desire.
3 Tries to detect thoughts and then ambush intruders; during the battle, it drops hints about useful information it possesses, which it will provide if you surrender
4 Its evil plans are too far advanced to risk any trouble; it tries to escape if interfered with
5 Meeting with one of its aboleth thralls , a well-known human or merfolk noble; they will kill you to preserve their secret
6 In its lair, monologuing about how it is one of the last of a species beyond age, knows secrets beyond mortal ken, has been banished by treacherous gods, etc.; its monologue lasts until killed
1 A projected image of the nearby aboleth; it promises you information or treasure in exchange for your promise to perform a task on the surface world or to kill a rival monster
2 An aboleth thrall that tries to lead you towards or away from the aboleth’s lair
3 A telepathic vision of you swimming into a nearby underwater cave and finding treasure
4 Wet footprints lead to a dying humanoid, diseased by an aboleth tentacle; it’s gasping out its last, unable to breathe air.
Aboleths dwell among the ruins of forgotten cities in underground lakes or at the bottom of the sea.
CR 11–16 Aboleth ; aboleth and 1 or 2 thralls ; aboleth and 1 or 2 merrow ; aboleth and sea hag or siren (see harpy).
Treasure 170 pp, 600 ep, platinum statuette of a three-eyed piscine humanoid (900 gp), gold crown for a Large creature (750 gp), 2 potions of water breathing that also allow water-breathing creatures to breathe air, periapt of health
CR 17–22 Aboleth and 1d4 + 1 thralls ; aboleth and 1 or 2 chuuls
Treasure 6,000 gp, 30 scattered pearls (100 gp each), 2 potions of supreme healing , folding boat , staff of charming
CR 23–30 Aboleth and 1d4 + 5 thralls ; aboleth and 3 chuuls ; ancient aboleth and 1d4 thralls
Treasure 500 bars of gold stamped with the name of a legendary empire (50 gp each), life-sized silver statue of a sea elf (7,500 gp), apparatus of the crab , rod of lordly might
Aberrations are unnatural beings that don’t belong to this plane of existence. Many aberrations are telepathic and use a mental power known as psionic power instead of magic. An aboleth is an aberration.