Zombie apoc simulator

When you attack an object with this magic sword and hit, maximize your weapon damage dice against the target. When you attack a creature with this weapon and roll a 20 on the attack roll, that target takes an extra 4d6 slashing damage. Then roll another d20. If you roll a 20, you lop off one of the target's limbs, with the effect of such loss determined by the GM. If the creature has no limb to sever, you lop off a portion of its body instead. In addition, you can speak the sword's command word to cause the blade to shed bright light in a 10 foot radius and dim light for an additional 10 feet. Speaking the command word again or sheathing the sword puts out the light.