Walker

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 walker drops to 1 hit point instead.

Undead Virus. When a target is infected with this virus there hit point maximum drops by 1 every hour until death, upon death the creature turns into a walker unless there brain is destroyed. This infection can only be stopped by amputating the limb that was bit within 10 minutes of the bite. There is no cure for this virus.

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

Bite. Melee Weapon Attack: +3 to hit, one target. Hit: 4 (1d6 + 1) piercing damage and 6 (1d10) necrotic damage. upon a successful hit the target must make a DC 8 constitution saving throw, on a success nothing happens, on a failure the target is infected with the Undead Virus.