Parasitic Sense. The writhing abomination can sense any living creature within 60 ft regardless of sight or sound.

Multiattack. The writhing abomination makes two attacks: one with its tentacles and one with its maw.

Tentacles. Melee Weapon Attack: +4 to hit, reach 10 ft., one creature. Hit: 12 (2d8 + 2) piercing damage, and the target must succeed on a DC 15 Dexterity saving throw or be grappled (escape DC 15). If the target is Medium or smaller, it is also restrained until this grapple ends. While grappling the target, the writhing abomination has advantage on attack rolls against it and can’t use this attack against other targets. When the writhing abomination moves, any Medium or smaller target it is grappling moves with it.

Maw. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 2) piercing damage and 4 (1d6) Acid Damage.

Adaptive Grafting. If there are items nearby to do so, the writhing abomination may graft such item onto their body to add +2 to their AC until the start of their next turn.

Infestation.  If a target grappled by a writhing  abomination falls to 0 hit points, the writhing abomination will begin to graft with the target. The target makes death saving throws at disadvantage while being infested. Upon failing all three death saves, the writhing abomination will burrow into and replace the target's nervous system, and the target dies, becoming a Marionette.