Collective Corpse

Undead Fortitude. If damage reduces the creature 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 creature drops to 1 hit point instead.

Decomposing Corpses. When laying still, Collective Corpses are indistinguishable from regular mass graves.

Slam. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 6 (1d8 + 1) bludgeoning damage.

Claw Sweep. Melee Weapon Attack: +3 to hit, reach 5ft., 5 ft. radius. Hit: 10 (1d10+2) slashing damage.

Spawn Zombie. Collective Corpses can loosen one of the many corpses it is made up of, and spawn a regular zombie, it takes 1d4 damage from this. On the start of the collective corpses turn, if it rolls a 5 or 6 on a d6, it recharges this ability.

Grab. Once per round, when attacked with any melee attack, Collective Corpses can attempt to grab the attacker. The attacker must make a dexterity saving throw with a DC of 15. On a fail, one or more of the many arms grabs the attacker, and they are considered restrained.

At the end of the attackers turn each round, they may attempt to break free by rolling a strength check contesting the Collective Corpse, or a party member can try to break them free by dealing 15 or more damage with one attack, breaking off the arm.