Amalgamation. The Abomination is the amalgamation of many different creatures and therefore cannot be stunned or incapacitated as a whole. However, specific creatures within the pile can be affected in this way, which might aid in escaping a grapple. 

Split. The Abomination can split itself into two entities. HP is halved, but stats remain the same. Each creature can make one attack and acts on the same initiative count. 

Absorb. When the Abomination hits with a melee attack the creature must make a DC 16 Dexterity Saving throw or be absorbed into the mass and receives the restrained condition. On their turn, the restrained creature can use their action to make another save to escape. If the creature remains restrained for three turns it is swallowed by the Abomination and is knocked unconscious. 

Multiattack. When the Abomination is whole, it can attack twice on its turn.

Wallop. Melee Weapon Attack: +10 to hit, reach 10 ft., 1 target. Hit: 16 (1d12 + 10) bludgeoning damage.

Spray. Ranged Weapon Attack: +10 to hit, range 30/60 ft., 2 targets. Hit: 14 (1d8 + 10) piercing damage.