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

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

Undead Fortitude. If damage reduces the hoard to 0 hit points, the hoard 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.

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.

Multiattack. The hoard can make up to two melee weapon attacks.

Gnaw and Claw. Melee Weapon Attack: +5 to hit, reach 5 ft., up to two targets. Hit: 7 (1d8 + 5) slashing damage. 

Pull Under. Melee Weapon Attack: +5 to hit, reach 5 ft., up to two targets. Hit: 8 (1d8 + 5) slashing damage. On a hit a creature must succeed a DC 14 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 14 at the start of each of their turns.

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: +5 to hit, reach 5 ft., up to two targets. Hit: 5 (1d6 + 5) slashing damage.

Pull Under (Split). Melee Weapon Attack: +5 to hit, reach 5 ft., up to two targets. Hit: 5 (1d6 + 5) slashing damage. On a hit a creature must succeed a DC 14 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 14 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, whether split or whole, can make one attack with advantage against one creature it chooses that is within itself. Melee Weapon Attack: +5 to hit, reach 5 ft., any target within the hoard. Hit: 7 (1d8 + 5) slashing damage.

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