Undead Fortitude: If damage would reduce the Shambler to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless it is fire or from a critical hit. On a success, the Shambler drops to 1 hit point instead.

Horde Tactics: If the Shambler is engaged in melee combat with a creature and there is at least one other undead within 5ft of that creature, the Shambler makes all attacks and grapple checks with advantage.

Zombie Virus: When an undead creature with this ability makes a successful bite attack on a creature, that creature potentially becomes infected with the virus and eventually turning into an undead themselves. If the bitten creature makes the saving throw, then the bite did not break flesh. If the bitten creature fails the save, the DM rolls a d6 to determine the location of the bite. Every 24 hours after the bite, the afflicted creature takes 1d4 Constitution damage. This damage is irreversible and once the creature’s Constitution score falls to 0 from this effect, they die and turn into a zombie within 3d12 minutes. If the bite is determined to be on a limb and that limb is severed within 1 minute of the bite, the creature is unaffected by the virus.

D6 Location:

1-Left Arm

2-Right Arm

3-Left Leg

4-Right Leg

5-Torso

6-Head/Neck