Legendary Resistance (3/day). When the Aboleth fails a saving throw, it can choose to succeed instead.

Amphibious. The aboleth can breathe air and water.

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.

Aversion to Dragonfire. If the aboleth is a target of an attack that deals Dragonfire damage, that attack is made at advantage.

Magic Resistance. The Abominable Aboleth has advantage on saving throws against spells and other magical effects

Siege Monster. The Abominable Aboleth double damage to objects and structures

Root Source: When the Abominable Aboleth hits a creature with a melee weapon attack, that creature must succeed on a DC 15 Constitution saving throw. On a failure, they contract Astral Infection.

Multiattack. The aboleth makes one tentacle attacks, one claw attack, and one attack with its Chilling Gaze

Tentacle. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 12 (2d6 + 5) bludgeoning damage. The target must succeed on a DC 10 Constitution saving throw or contract Astral Infection.

Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 14 (2d6 + 7) slashing damage plus 7 (2d6) cold damage. The target must succeed on a DC 15 Constitution saving throw or contract Astral Infection.

Chilling Gaze. The  grafted yeti targets one creature it can see within 30 feet of it. If the target can see the yeti, the target must succeed on a DC 13 Constitution saving throw against this magic or take 10 (3d6) cold damage and then be paralyzed for 1 minute, unless it is immune to cold damage. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If the target’s saving throw is successful, or if the effect ends on it, the target is immune to the Chilling Gaze of all yetis for 1 hour

Enslave (1/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.

Tentacle Swipe. The aboleth makes one tentacle 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.

The Abominable Aboleth only has one mythic action, and can only use it at the end of a creatures turn. It regains this mythic action after a long rest.

Plane Shift. The Abominable Yeti casts Plane Shift on itself.