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```statblock
monster: Aboleth
```
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*Large aberration, lawful evil*
**Armor Class** 17 (natural armor)
**Hit Points** 135 (18d10+36)
**Speed** 10 ft., swim 40 ft.
| STR | DEX | CON | INT | WIS | CHA |
|---------|--------|---------|---------|---------|---------|
| 21 (+5) | 9 (-1) | 15 (+2) | 18 (+4) | 15 (+2) | 18 (+4) |
**Saving Throws** Con +6, Int +8, Wis +6
**Skills** History +12, Perception +10
**Senses** darkvision 120 ft., passive Perception 20
**Languages** Deep Speech, telepathy 120 ft.
**Challenge** 10 (5,900 XP)
***Amphibious***. The aboleth can breathe air and water.
***Mucous Cloud***. While underwater, the aboleth is surrounded by transformative mucus. A creature that touches the aboleth or that hits it with a melee attack while within 5 feet of it must make a DC 14 Constitution saving throw. On a failure, the creature is diseased for 1d4 hours. The diseased creature can breathe only underwater.
***Probing Telepathy***. If a creature communicates telepathically with the aboleth, the aboleth learns the creature's greatest desires if the aboleth can see the creature.
***Multiattack***. The aboleth makes three tentacle attacks.
***Tentacle***. *Melee Weapon Attack:* +9 to hit, reach 10 ft., one target. *Hit:* 12 (2d6+5) bludgeoning damage. If the target is a creature, it must succeed on a DC 14 Constitution saving throw or become diseased. The disease has no effect for 1 minute and can be removed by any magic that cures disease. After 1 minute, the diseased creature's skin becomes translucent and slimy, the creature can't regain hit points unless it is underwater, and the disease can be removed only by *[[heal]]* or another disease-curing spell of 6th level or higher. When the creature is outside a body of water, it takes 6 (1d12) acid damage every 10 minutes unless moisture is applied to the skin before 10 minutes have passed.
***Tail***. *Melee Weapon Attack:* +9 to hit, reach 10 ft. one target. *Hit:* 15 (3d6+5) bludgeoning damage.
***Enslave (3/Day)***. The aboleth targets one creature it can see within 30 feet of it. The target must succeed on a DC 14 Wisdom saving throw or be magically [[Charmed]] by the aboleth until the aboleth dies or until it is on a different plane of existence from the target. The [[Charmed]] target is under the aboleth's control and can't take reactions, and the aboleth and the target can communicate telepathically with each other over any distance.
Whenever the [[Charmed]] target takes damage, the target can repeat the saving throw. On a success, the effect ends. No more than once every 24 hours, the target can also repeat the saving throw when it is at least 1 mile away from the aboleth.
The aboleth can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The aboleth regains spent legendary actions at the start of its turn.
**Detect**. The aboleth makes a Wisdom (Perception) check.
**Tail Swipe**. The aboleth makes one tail attack.
**Psychic Drain (Costs 2 Actions)**. One creature [[Charmed]] by the aboleth takes 10 (3d6) psychic damage, and the aboleth regains hit points equal to the damage the creature takes.