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

Aura of Decay.
At the start of each of the Wretchspawn’s turns, all non-undead creatures within 10 feet take 10 (3d6) necrotic damage.

Soul Rot.
When the Wretchspawn kills a creature, its soul is partially devoured. The next time the Wretchspawn deals necrotic damage, it deals an additional 10 (3d6) necrotic damage and the target must succeed on a DC 18 Constitution saving throw or be cursed (disadvantage on death saving throws for 1 hour).

Multiattack.
The Wretchspawn makes two Necrotic Lash attacks.

Necrotic Lash.
Melee Weapon Attack: +10 to hit, reach 10 ft., one creature.
Hit: 27 (5d8 + 3) necrotic damage. The target must succeed on a DC 18 Constitution saving throw or its maximum hit points are reduced by the amount of necrotic damage dealt until a long rest.

Blight Burst (Recharge 5–6).
The Wretchspawn expels corrupted soul matter in a 30-foot cone. Each creature in that area must make a DC 18 Dexterity saving throw, taking 56 (16d6) necrotic damage on a failed save, or half as much on a success. Creatures that fail are also blinded for 1 minute.

Wriggle Through.
The Wretchspawn squeezes through a creature’s space. Choose a creature within 5 feet; it must succeed on a DC 18 Dexterity saving throw or take 14 (4d6) necrotic damage and fall prone.

Rotten Retort.
When hit by a melee attack, the Wretchspawn can release a burst of decayed flesh. The attacker must succeed on a DC 18 Constitution saving throw or be poisoned until the end of its next turn.

Soul Echo (1/Day).
If the Wretchspawn is reduced to 0 HP, it can instead drop to 1 HP and become ethereal until the end of its next turn.