Corpse Fiend

Corpse Heap. This creature reduces any non-magical damage attack by 1d8. 

Flesh Eater. When the Corpse Fiend reduces a creature to 0 hit points, it can use a bonus action to consume the corpse restoring 3d6+5 damage. If the target is a player, they must succeed a DC 18 constitution save or be bitten into pieces and swallowed.

Multi attack. The Corpse Fiend makes three attacks, one with its cursed spear and two with its rusted claw. It can use its phlegm cannon in place of all of its attacks.  

Cursed Spear. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 18(4d6+4) piercing damage. The target must succeed a DC 15 constitution save or gain the effects of Bestow Curse using constitution as the ability score. 

Rusted Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11(2d6+4) slashing damage. If hit, the target creature must make a DC 14 constitution saving throw or take an additional 11(2d6+4) poison damage.

Phlegm Cannon. Ranged Weapon Attack: range between 35-350 ft., unlike a normal attack, instead choose a point within range. Any creature within a 20 ft. diameter must make a DC 16 constitution saving throw taking 32(7d6+7) poison damage on a failed save or half as much on a successful one. An area of slime is left in the area and counts as difficult terrain. 

Rotting Construct. The volatile body of this creature causes it to rupture if it take more than 20 damage in one turn after Corpse Heap is applied. All creatures within 5 ft. of the Corpse Fiend must make a DC 14 dexterity saving throw taking 7(2d6) bludgeoning damage on a failed save or half as much on a successful one.