Weapon (Greathammer), legendary (requires attunement)
Hammer of the Forge
This magic greathammer grants a +2 bonus to attack and damage rolls made with it and it has the reach property. Whenever Forgebreaker hits an object, the hit is a critical hit. When you score a critical hit on a creature that is wielding a metal weapon, you break the target's weapon unless it is magical. If the target's weapon is magical, the target has to succeed on a contested check with DC equal to 8+your proficiency bonus+your strength modifier. The roll for the wielder of the weapon is 1d20+(1*the rarity of the magic item). On a failed save the magic weapon breaks. This damage cannot be fixed by nothing short of a Wish spell.
A creature has disadvantage on attack rolls made with Forgebreaker unless their size is huge or larger. Additionally, a creature that is large or smaller must have a strength strength score of 23 or higher to wield this greathammer.
Forgebreaker is one part of the Tools of the Dragon Lords alongside Guthix's Anvil and is capable of forging and destroying Orbs of Dragonkind when used in conjunction it.