Warhammer of Eruptions

Weapon (warhammer), rare (requires attunement)

This sturdy warhammer has a core of magma at its center that heats up during combat. You gain a +1 bonus to attack and damage rolls made with this magic weapon.

Eruption. The first time that the warhammer hits a target in combat, it starts to release a steady stream of embers and smoke. When this happens, and while the hammer is smoldering in this way, it deals an extra 1d6 fire damage to any target it hits. At the end of each of your turns while the hammer is smoldering, its fire becomes increasingly unstable. At the end of the third turn, the hammer erupts, spraying lava and releasing a volcanic storm from it in a 30-foot cone in a direction of your choice (no action required). Each creature in the area must succeed on a DC 13 Dexterity saving throw, taking 3d6 fire damage and 3d6 lightning damage on a failed save, or half as much damage on a successful one. The lava then vanishes. The warhammer cools and doesn’t erupt if combat ends or if you drop or stow the weapon before it erupts. Once the warhammer erupts, it loses this property until 2d6 hours have passed.

The volcano melts mountains, burns civilizations, and leaves only ash in its wake. In its destruction, there is infinite potential for something new to be reborn.