Blood Memory (Aura).
Any creature that starts its turn within 20 feet of the sludge must succeed on a DC 17 Wisdom saving throw or relive a traumatic betrayal. On a failure, the creature suffers disadvantage on Wisdom and Charisma checks and saving throws for 1 minute. If already affected, it instead takes 4d6 psychic damage per round it remains in the aura. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Coagulate Form (Recharge 5–6).
As a reaction to taking physical damage, the sludge can harden its mass, gaining +5 AC until the start of its next turn.

Amorphous.
The sludge can move through a space as narrow as 1 inch wide without squeezing.

Pseudopod. Melee Attack Roll: +4, reach 5 ft. Hit: 12 (3d6 + 2) Acid damage.

Engulf in Guilt.
Melee Weapon Attack: +9 to hit, reach 10 ft., one target.
Hit: The target must make a DC 16 Dexterity saving throw or be engulfed. An engulfed creature is restrained, and takes 3d6 acid + 2d6 necrotic + 2d6 psychic damage at the start of each of its turns. While engulfed, the creature must make a DC 17 Wisdom saving throw at the start of each of its turns or become stunned until the end of that turn. A creature can escape by succeeding on a DC 18 Strength check as an action.

Sanguine Pulse (Recharge 5–6).
The sludge pulses with infernal blood magic. Each creature within 20 feet must make a DC 18 Constitution saving throw. On a failed save, a creature takes 5d8 necrotic damage, is knocked prone, and begins bleeding, taking 1d4 necrotic damage at the start of each of its turns for 1 minute. A creature can make a DC 15 Constitution save at the end of each of its turns to end the bleeding.

Blood Feast.
The sludge targets one creature it is currently engulfing that is stunned, frightened, or paralyzed. That creature takes 6d6 necrotic damage, and the sludge regains HP equal to the damage dealt.