Void Tendrils. The abomination can have up to two tendrils at a time. Each tendril can be attacked (AC 18; 15 hit points; immunity to poison and psychic damage). Destroying a tendril deals no damage to the abomination, which can manifest replacement tendrils at the end of its next turn. A tendril can also be broken if a creature takes an action and succeeds on a DC 15 Strength check against it.

Shadowy Form: Whenever the abomination takes the Hide action when it is in dim or dark light it has advantage.

Amphibious. The abomination can breathe both air and water.

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

Spider Climb. The abomination can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Multiattack. The abomination makes two attacks with its void tendrils, or one with its void tendril and another with its bite.

Bite. Melee Weapon Attack: (+7) to hit, reach 5 ft., one target. (Hit: 2d8+4) piercing damage and must succeed on a DC 14 Constitution saving throw or be poisoned for 1 minute. Until this poison ends, the target is paralyzed. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Void Tendril. Melee Weapon Attack: (+7) to hit, reach 40 ft., one target. Hit: (1d8+4) bludgeoning damage. If the target is a Large or smaller creature, it is grappled (escape DC 14). Until this grapple ends, the target is restrained, and the abomination can’t use this tendril on another target (the abomination has two tendrils). If this attack is a critical hit, the target also can’t breathe or speak until the grapple ends.

Pull. The abomination pulls a creature grappled by it up to 20 feet straight toward it and makes a bite attack. When the creature moves within 5 ft. of an ally of that creature, that ally must succeed on a DC 12 Wisdom saving throw or be forced to use their reaction to make an attack against that creature as if they were making an opportunity attack. This can only happen once per turn when this action is taken.