Reckless. If the abomination chooses to at the beginning of its turn, it can gain advantage on all attack rolls until the end of its turn. However, all attacks until the beginning of its next turn have advantage.

Painful Strikes. The abomination deals an additional 4 (1d8) psychic damage with its strikes.

Tyrannical Aura. A creature has disadvantage on concentration checks while within 60 ft. of the abomination, and when it loses concentration it takes 2 (1d4) points of psychic damage per level of spell lost.

Savage Attacker. If the abomination reduces a creature to zero hit points, it can immediately use its bonus action to move up to half of its movement and make an attack against a separate creature.

Amalgamation. If the abomination takes more than 25 points of piercing or slashing damage, it sprouts another arm at the beginning of its next turn. This ability does not function if the abomination has taken radiant or fire damage between the instance of piercing or slashing damage and the beginning of its next turn.

Multiattack. The abomination makes at least two attacks: one with its claws or bite, and one attack per arm it has.

Adamantine Claws. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 20 (3d8 + 7) slashing damage plus 4 (1d8) psychic damage. Any attack against a structure is considered a critical hit with this attack. 

Bite. Melee Attack: +13 to hit, reach 5 ft., one target the abomination has grappled currently. Hit: 28 (6d6 + 7) piercing damage plus 4 (1d8) psychic damage and the target is swallowed. While swallowed, the target is blinded, restrained, and cannot breathe. At the beginning of each of the target's turns, it takes 21 (6d6) force damage. If the abomination takes more than 40 points of damage in a single turn, it must succeed on a DC 22 Constitution saving throw or regurgitate the target.

Arm Bludgeon. Melee Attack: +13 to hit, range 5 ft., one target. Hit: 12 (1d10 + 7) bludgeoning damage plus 4 (1d8) psychic damage.

Impervious Hide. When a creature misses the abomination with an attack roll but still rolls higher than a 15 on the attack, the abomination can magically cause the attack to instead attack a creature within range of the creature who made the attack. The creature must make another attack roll against the new target.