Rumble Hammer

Weapon (light hammer), rare (requires attunement)

This hammer sports shaft and head of stone. You gain a +1 bonus to attack and damage rolls made with the hammer. In addition, when you strike a target that is standing on the ground, a loud rumble echoes between the stone head of the rumble hammer and the ground, dealing 1d6 thunder damage to the target. On a critical hit against a creature touching the ground, the target instead takes 2d6 thunder damage and must make a DC 15 Strength saving throw or be forced prone.

As an action once per day, the hammer can be struck against the ground or a similarly hard surface to create a thunderwave, using Strength as your spellcasting ability modifier.