Undead fortitude:If damage reduces the abomination to 0 hit points, it must make a Constitution saving throw with a DC of 5 + half  the damage taken, unless the damage is radiant or from a critical hit. On a success, the abomination drops to 15 hit points instead.

 Regenerating mass: The abomination regains 15  hit points at the start of each of its turns. this effect is stalled for one round if the abomination takes fire or necrotic damage.

Multi attack.The abomination attacks three times with its slam.

Slam. Melee Weapon Attack: +9 to hit, reach 20 ft., 1 target. Hit: 27 (4d8 + 9) bludgeoning damage. 

Horrific abomination: As a bonus action the abomination can force one creature that can see it within 45 ft to make a  wisdom saving throw (DC 17) or take 3d6 psychic damage and be frightened for one minute. the frightened creature can repeat its saving throw at the end of each of its turns.

Hulking protector: if the abominations creator takes any form of damage the abomination can as a reaction shield the creature with its own body. And the abomination takes the damage instead.