Forge Breaker (5e Equipment)

Weapon (any hammer), rare (requires attunement)

You gain a +2 bonus to attack and damage rolls made with this magic weapon. When you score a critical hit with it, it creates a thunderous boom audible out to 300 feet and, if the target is wielding a nonmagical metal weapon, you begin to break the target's weapon. The weapon takes a permanent and cumulative -1 penalty to damage rolls. If this penalty drops to -5, the weapon is destroyed. This damage can't be repaired except by magic such as the mending cantrip or another magic item.