While editing the max-health property, just spam the numeric keys on your keyboard repeatedly till as long as you like. Also, set the health property to be the same as the max-health property.
This way, if the player takes exactly 100 damage they will just die. It’s best to also add a line like: Humanoid:SetStateEnabled(Enum.HumanoidStateType.Dead,false)
This line ensures that the rig won’t die at all. This way, you wouldn’t even need to use that hacky method of yours, just insert a script in the humanoid and run that line.
^ Basically nullifies any damage taken by the NPC. You can also disable the Dead humanoid state.
And I recommend setting the MaxHealth to something high, like math.huge as someone else suggested