Bloated Corpse

Corpse explosion. When the bloated corpse is dropped to 0 hp, it explodes in a bloody mess of bile and ichor. each creature within 10 ft. must succeed on a DC 15 Dexterity Saving Throw taking 2d6 poison damage on a failed save or half as much on a successful save. 

Stench. Any creature that starts its turn within 5 ft. of the Bloated Corpse must succeed on a DC 10 Constitution saving throw or be poisoned until the start of its next turn. On a successful saving throw, the creature is immune to the Bloated Corpse's Stench for 24 hours.

Turn Defiance. The Bloated Corpse and any undead within 30 ft. of it have advantage on saving throws against effects that turn undead.

Grub Swollen. When a Bloated Corpse is reduced to 0 hit points, it violently splits open, disgorging 4 Swarms of Rot Grubs in a 10 foot radius. Any creature within the 10 foot radius at the time of disgorging becomes infected with 1d4 rot grubs. 

At the start of each of the target’s turns, the target takes 1d6 piercing damage per rot grub infesting it. Applying fire to the bite wound before the end of the target’s next turn deals 1 fire damage to the target and kills these rot grubs. After this time, these rot grubs are too far under the skin to be burned.

If a target infested by rot grubs ends its turn with 0 hit points, it dies as the rot grubs burrow into its heart and kill it. Any effect that cures disease kills all rot grubs infesting the target.

The Swarms of Rot Grubs fight until defeated.

Multiattck. The Bloated Corpse can make two claw attacks in one turn, or one Bite attack on a grappled target.

Grapple. The Bloated Corpse attempts to grapple one target within 5 ft. of it that has the size of medium or smaller. The target must make a contested Athletics or Dexterity check to dodge the attack. The Bloated Corpse has advantage on this attack if the target is within 5 ft. of an enemy.  

Bite. Melee Weapon Attack: +5 to hit, range 5 ft., 1 target. Hit: 14 (2d8 + 5) [piercing] damage plus 13 (3d8) poison damage.

Claw. Melee Weapon Attack: +3 to hit, range 5 ft., 1 target. Hit: 10 (2d6+3) slashing damage.