Atrexa Grand Aboleth

Amphibious. The aboleth can breathe air and water.

Legendary Resistance (3/Day, or 4/Day in Lair). If the aboleth fails a saving throw, it can choose to succeed instead.

Mucus Cloud. While underwater, the aboleth ancient is surrounded by transformative mucus. A creature that touches the Atraxa or that hits it with a melee attack while within 15 feet of it must make a DC 20 Constitution saving throw. On a failure, the creature is diseased for 1d4 hours. The creature becomes coved in a slimy substance.

The disease has no effect for 2 rounds and can be removed by any magic that cures disease. After 12 seconds, 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 a disease-curing spell of 6th level or higher. When the creature is outside a body of water, it takes 6 (1d12) acid damage every 1 minute unless moisture is applied to the skin before 1 minute has passed.

Probing Telepathy. If a creature the aboleth can see communicates telepathically with the aboleth, the aboleth learns the creature’s greatest desires.

Multiattack. The aboleth makes two Tentacle attacks and uses either Dominate Mindor mucise breath if available or it can preform a spell.

Tentacle. Melee Attack Roll: +11, reach 15 ft. Hit: 21 (5d6 + 12) Bludgeoning damage. If the target is a Large or smaller creature, it has the Grappled condition (escape DC 16) from one of four tentacles.

Dominate Mind (2/Day). Wisdom Saving Throw: DC 16, one creature the aboleth can see within 30 feet. Failure: The target has the Charmed condition until the aboleth dies or is on a different plane of existence from the target. While Charmed, the target acts as an ally to the aboleth and is under its control while within 60 feet of it. In addition, the aboleth and the target can communicate telepathically with each other over any distance.

The target repeats the save whenever it takes damage as well as after every 24 hours it spends at least 1 mile away from the aboleth, ending the effect on itself on a success.

Mucise Breath (Recharge 5–6). Dexterity Saving Throw: DC 18, each creature in a 60-foot-long, 10-foot-wide Line. Failure: 54 (12d8) Acid damage. Success: Half damage. Targets need to preform a DC 20 Con sav. On a failure, the creature is diseased for 1d4 hours. The creature becomes coved in a slimy substance.

Frightful Presence. Each creature of the aboleth ancient noble's choice that is within 120 feet of the aboleth ancient noble and aware of it must succeed on a DC 19 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the aboleth ancient noble's Frightful Presence for the next 24 hours.

Spellcasting. Altraxa casts one of the following spells, requiring no Material components and using Int as the spellcasting ability (spell save DC 17, +9 to hit with spell attacks):

Any time: Shape water, Vicious Mockery, Staggering Smite, Controle Water

1/day each: Tidal Wave, Mental Prison, Feeblemind, Psychic scream, Storm of Vengeance

Godscale (Recharge 3-6). As a bonus action at the end of its turn, Altraxa pulses with unstable far realm energy. All creatures within 15 feet of the aboleth or within 30 feet if looking in its direction must make a DC 19 Wisdom saving throw. On a failed save, a creature takes 6d6 psychic damage and takes a -1 penalty to attack rolls, ability checks and saving throws. This effect can stack up to a cap of -6 and lasts until the creature completes a long rest. 

Legendary Action Uses: 3 (4 in Lair). Immediately after another creature’s turn, the aboleth can expend a use to take one of the following actions. The aboleth regains all expended uses at the start of each of its turns.

Lash. The aboleth makes one Tentacle attack.

Psychic Drain. If the aboleth has at least one creature Charmed or Grappled, it uses Consume Memories and regains 10 (2d10) Hit Points. Dealing that damage to the target.