Swarm. The hoard can occupy another creature’s space and vice versa, and the swarm can move through any opening large enough. The swarm can’t regain hit points or gain temporary hit points.

Unusual Nature. The hoard does not need to eat, drink, breathe, or sleep.

Turn Resistance. The hoard has advantage on saving throws that would Turn Undead.

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

Reactive. The hoard can take one reaction on every turn in combat.

Mindless Strength. The hoard will continue to attack as if still at full strength until it is completely destroyed.

Multiattack. The hoard can make up to four melee attacks.

Gnaw and Claw. Melee Weapon Attack: +8 to hit, reach 5 ft., any target within range or within the hoard. Hit: 24 (5d8 + 8) slashing damage. 

Pull Under. Melee Weapon Attack: +8 to hit, reach 5 ft., any target within range. Hit: 22 (4d8 + 8) slashing damage. On a hit a creature must succeed a DC 18 contested Strength save, on a fail the creature is dragged into the hoard and is considered restrained and prone. The creature can reattempt the contested strength save DC 18 at the start of each of their turns.

Terrifying Gaze. Each creature within 30 ft. of the hoard must succeed a DC 18 Constitution saving throw or be paralyzed with fear. A paralyzed creature is unable to move and all attacks made within 5 ft. of the creature are considered critical hits. All attacks are made with advantage against the creature. A successful repeat of the Constitution saving throw on any of their next turns will break the paralysis and the creature is immune for the next 24 hours.

Split. The hoard can choose to split into 1d3+1 huge hoards which share the same initiative count but will have hit points equating to their initial max hit points divided by the number of smaller hoards rounded down. A split-off hoard can make all the same actions and reactions as the hoard as a whole.

Gnaw and Claw (Split). Melee Weapon Attack: +8 to hit, reach 5 ft., any target within range or within the hoard. Hit: 17 (3d8 + 8) slashing damage. 

Pull Under (Split). Melee Weapon Attack: +8 to hit, reach 5 ft., any target within range. Hit: 19 (2d8 + 8) slashing damage. On a hit a creature must succeed a DC 18 contested Strength save, on a fail the creature is dragged into the hoard and is considered restrained and prone. The creature can reattempt the contested strength save DC 18 at the start of each of their turns.

Rejoin. The split-off hoards can rejoin back together action if they are all within 5 ft. of at least one other hoard, merging their current hit points to create a new hit point maximum.

Weight of the Hoard. The hoard can make one attack with advantage against one creature it chooses that is within itself. Melee Weapon Attack: +8 to hit, reach 5 ft., any target within the hoard. Hit: 12 (1d8 + 8) slashing damage.

Surge. The hoard can move 5 ft. towards a creature that dealt damage to it.