This mod adds one thing and one thing only: A new game rule:
multiplicativeDamageIncrease
This game rule, when set, will multiply base damage taken by the value specified.
If set to 2, a zombie will deal 6 damage instead of 3, and if set to 0, a zombie will do 0 damage instead of 3.
By default, the game rule is set to 1 (normal base damage), but can be configured before world creation or with cheats.