Avalanche Hammer

Weapon (maul or warhammer), very rare

This frigid hammer carries a block of unmelting ice from the Everglacier encased in steel. This magic weapon deals an extra 1d4 cold damage to any target it hits, or 2d4 if the target is prone.

The hammer grows colder with each strike it makes, which are represented with charges. Each time you hit a creature with the hammer, it gains 1 charge, up to a maximum of 5. An unused charge is lost after 1 minute.

Avalanche. If the hammer has 5 charges, you can slam it on the ground in place of one of your attacks as part of the Attack action, expending all its charges and releasing a pummeling wave of snow and ice in a 15-foot cone. Each target in the cone must make a DC 15 Strength saving throw. On a failed save, a creature takes 3d6 bludgeoning damage and 3d6 cold damage and is pushed up to 10 feet away from you and knocked prone. Once this property has been used, the hammer can't gain charges again until 10 minutes have passed.

The mountains come crumbling down when I shake them.