Charge: bludgeoning damage. The abomination takes it's turn to ready a charge, picking a direction as it plants its hands and feet. On it's next turn it unleashed it's full might in one burst. Moving up to 70 feet in a straight line. Any creature in its path must succeed on a DC 16 dex save or take 3D6 +4 damage (half as much on a success) and fall prone.  If it hits a strong physical barrier during the charge or at the very end. (wall or stone column), or if it catches fire during the charge, its movement is stopped and it falls prone, and takes 3D6 +4 damage. ( or fire damage)

Necrotic Presence: the undead abomination exudes an unnerving foul aura. Creatures that start or end their turn within 15 feet of it must make a constitution saving throw, (DC 16) taking 2D6 poison damage and becoming poisoned for 1D4+1 rounds on a fail. (half with no poison effect on a save)

Multiattack: The abomination either takes it's charge action, or 3 claw attacks, or one slam attack and 1 sludge bomb, or 2 claws and 1 sludge bomb

Slam: : +4 to hit, reach 5 ft., 1 target. Hit: (2d8 + 4) bludgeoning  damage. The abomination slams two massive fists onto the ground, causing damage to a target and anyone in 10 feet range

Claws: +4 to hit, reach 5 ft, 1 target. Hit: (1D6 + 4) necrotic damage, claws on smaller arms or exposed jagged bones, secreting the same black sludge, rake across one target.

Sludge bomb: : +2 to hit, range 30 /50 ft., 1 target. Hit: (1d4 + 2) necrotic damage.  If a player is hit, they are stuck and considered grappled.  A successful DC 13 strength check will free the player, or in 3 turns.