Undead Fortitude. If damage reduces the zombie to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the zombie drops to 1 hit point instead.

Corpse Regeneration. If the Zombie Monstrosity ends its turn on any number of corpses it may add one corpse to it's body. Doing so adds 10 hit points to the Zombie Monstrosities hit point maximum and increases its Constitution score by one. The Zombie monstrosity begins with twenty five corpses.

Grasping Hands. Any creature that ends its turn within 5 feet of the Zombie Monstrosity must make a Strength or Dexterity saving throw DC15. On a fail target creature becomes restrained.

Multiattack.  The Zombie Monstrosity makes three attacks: one with its consume and two with its slam.

Slam. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 4 (1d10 + 4) bludgeoning damage.

Consume. Melee Weapon Attack: +6 to hit, reach 5 ft, one target. Hit: (1d10 + 4) bludgeoning damage. If hit, target makes a Strength or Dexterity saving throw DC15. If target is restrained the are automatically consumed. On a success target escapes consumption. On a fail target is consumed and takes 3d8 necrotic damage every turn it remains consumed. Target may continue to make Strength saving throws once per turn while consumed. If target falls to 0 hit points while consumed, target dies. Zombie Monstrosity may only consume one target at any given time.