Multiattack. The abomination can use its Frightful Presence. It then makes two attacks: one with its slam and one with its bite or tentacle.

Slam. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 22 (3d10 + 7) bludgeoning damage.

Bite. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 24 (3d12 + 7) piercing damage.

Tentacle. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 22 (3d10 + 7) bludgeoning damage. If the target is a creature, it must succeed on a DC 20 Strength saving throw or be grappled (escape DC 20). Until this grapple ends, the target is restrained, and the abomination can't use its tentacle on another target.

Frightful Presence. Each creature of the abomination's choice within 30 feet of it and aware of it must succeed on a DC 18 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.