Magic Resistance. The Aberrant Monstrosity has advantage on saving throws against spells and other magical effects.

Regeneration. The Aberrant Monstrosity regains 20 hit points at the start of its turn if it has at least 1 hit point.

Tight Squeeze. The huge Aberrant Monstrosity can compress itself and squeeze into or through a medium-sized space or passage as if it were difficult terrain.  It suffers no squeeze penalties to attacks or movement while within a large-sized space.

Multiattack. The Aberrant Monstrosity makes five attacks: four with its many Claws and either one Bite attack or one Tongues attack.

Bite. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 18 (4d4 + 8) piercing damage.

Claw. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 17 (2d8 + 8) slashing damage.

Tongues. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 19 (2d10 + 8) bludgeoning damage. If the target is a Medium or smaller creature, it is grappled (escape DC 22). The aberrant monstrosity has plenty of tongues but it can only grapple one target at a time.  While it has a creature grappled this way, it can not target any other creature with its Bite attack or use its Disconcerting Psychic Scream ability.

Disconcerting Psychic Scream (Recharge 5–6).  The Aberrant Monstrosity emmits a terrible and barely audible sound that pierces the minds of all intelligent non-aberrations within 100 ft.  All targets must make a Charisma saving throw DC 17 or take 5d6 psychic damage and be stunned until the end of their next turn.  Those who make the save take half damage and are not stunned.  

Dodgy Scamper. The Aberrant Monstrosity can move up to half its speed (25 ft.) as a bonus action.  Attacks against it while moving this way have disadvantage.

Snatch Back. When a creature escapes from the grapple of its Tongues, the Aberrant Monstrosity can use its reaction to make one Tongues attack at disadvantage to recapture its excaping victim.  If successful, it can not do bludgeoning damage to the target with this reaction, but the creature remains grappled instead of escaping.