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.

Mob. The mob has the following traits.

• The mob has resistance to all damage that affects a single target and is vulnerable to AOE damage that fully encompass the mob.
• The mob may move through other creature's spaces and end their turn there. While another creature is in the mob's space they are considered restrained. The creature may move with a DC 21 Athletics check.
• The mob may not be subject to any conditions unless they specifically affect all creatures in an area.
• When the mob reaches 0 hit points, it breaks, and 2d8 zombies take its place. These survivors have 1 level of exhaustion, and only have 10 hit points left.
• The mob may not regain health or receive temporary hit points.

Mob Mentality. The mob has advantage on saving throws for the frightened condition, as well as effects that turn undead.

Multiple Creatures. The mob may take a reaction per turn, rather than per round.

Multiattack. The horde makes five slam attacks. This is reduced to four attacks at 150 hit points, three attacks at 100 hit points, and two attacks at 50 hit points.

Slam. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 12 (3d6 + 2) bludgeoning damage and the target must make a DC 16 Athletics or Acrobatics check or be pulled into the swarm's space.