Undead Swarm Fortitude. The swarm fights at full
strength until it is completely destroyed.
Swarm. The swarm can occupy another creature's
space and vice versa. the swarm can move
through any opening large enough for a medium
zombie. The swarm can't gain
temporary hit points. the hoard is immune to effects with Wisdom or Charisma saving throws. the hoard can move with grappled creatures with no movement hindrance.
Multiattack. The horde uses its pull under ability on all creatures it can, then uses its gnaw and claw attack on all creatures inside.
Gnaw and Claw. Melee Weapon Attack: +14 to hit,
reach 0 ft., one target in the swarm’s space. Hit: 34
piercing damage, 34 slashing damage, and 34 bludgeoning damage.
Pull Under. The horde attempts to envelope a
creature within its space. The target must succeed
on a DC 23 Strength saving throw or be knocked
prone and considered grappled (escape DC 23) as
they are pinned to the ground under a sea of
zombies. This ability can only be used if the horde
is above half of its maximum hit points. Frightful Presence. Each creature within 120 feet of it and aware of it must succeed on a DC 23 Wisdom saving throw or become frightened for 5 minute. A creature can repeat the saving throw at the end of each of its turns, with disadvantage if the hoard is within line of sight, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the hoard's Frightful Presence for the next 24 hours.
The hoard can take 3 legendary actions, choosing from the options below. and can only make one at the end of another creature's turn. The hoard regains spent legendary actions at the start of its turn.
Gnaw and Claw (Costs 2 Actions). the hoard makes a Gnaw and Claw attack against 3 creatures.
Pull Under. the hoard makes a Pull Under attack against 2 creatures.
Move. the hoard can move up to half its movement speed