Decomposing Limbs. Whenever the zombie takes at least 5 bludgeoning or slashing damage at one time, roll a d20 to determine what else happens to it:

1–8: One leg is severed from the zombie if it has any legs left.

9–16: One arm is severed from the zombie if it has any arms left.

17–20: The zombie is decapitated.

A severed head has a maximum of 7 hp and a speed of 0 feet. It can make a bite attack, but only against a target in its own space. Attacks made by a severed head are at disadvantage, but may also be negated entirely at the DM's discretion. Attacks made against a severed head automatically hit.

The zombie’s speed is halved if it’s missing a leg. If it loses both legs, it falls prone. If it has both arms, it can crawl. With only one arm, it can still crawl, but its speed is halved. With no arms or legs, its speed is 0 feet, and it can’t benefit from bonuses to speed.

Death Disease. Whenever a living humanoid is bitten by the zombie it must succeed on a DC 15 CON saving throw or become infected by the Death Disease. An infected character loses 1 from its maximum hit point total every hour. Whether from the disease progression or by any other means, when current hp is reduced to zero the victim dies and rises again as another Zombie Walker in 1d4 minutes. A Greater Restoration cast before the victim's current hp reaches zero will halt the process and restore the normal hit point maximum following a long rest.

Multiattack. The zombie makes up to three attacks: one with its bite and one claw attack for each arm it currently has. 

Bite. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 3 (1d4 + 1) piercing damage.

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