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.

The Horde. Whenever a loud noise is made it summons an additional 1d4 zombies.

Slam. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) bludgeoning damage.

Claw. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) slashing damage. When a living creature is hit it must make a DC 10 Con save. On a failed save the creature becomes infected. While infected it loses 1 Max HP every day until it hits 0. When it dies the creature spawns back as a zombie immediately. The only way to remove the curse is to cast lesser restoration if the infection has only lasted for less than a week. Or if it has been longer than a week a Greater Restoration.