Keen Smell. The Abomination has advantage on Wisdom (Perception) checks that rely on smell.

Tactical Camouflage. The Abomination has advantage on Dexterity (Stealth) checks made to hide.

Shifting Form. The Abomination adapts changing to attack or defense form from it's base form. Costs full turn to change. 

Attack. Multiple tentacles emerge and it gains 4 attacks +8 to hit, reach 10 ft. Hit: 10 (1d8+7)

Defense. Gain +5 ac and advantage on strength and constitution saving throws. Attacks change to 1 circular blast of Acid (recharge 5-6) DC 16 Constitution save or take 10 (2d10) acid damage. 

Multiattack. The Abomination can use its Acid Breath and makes two claw attacks.

Claw. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 14 (2d6 + 7) slashing damage plus 4 (1d6) acid damage.

Acid Breath (Recharge 6). The Abomination exhales a 15-foot cone of Acid. Each creature in that area must make a DC 18 Constitution saving throw, taking 20 (4d10) Acid damage on a failed save, or half as much damage on a successful one.

Mold Self. The Abomination can shift it's form around to mitigate damage, it can reduce the damage by 1d12 once per round.