Source: Explorer's Guide to Wildemount

Weapon (warhammer), very rare (requires attunement)

This item takes the form of a leather-wrapped metal rod emblazoned with the symbol of Pelor, the Dawn Father. While grasping the rod, you can use a bonus action to cause a warhammer head of crackling radiance to spring into existence. The warhammer's radiant head emits bright light in a 15-foot radius and dim light for an additional 15 feet. The light is sunlight. You can use an action to make the radiant head disappear.

While the radiant head is active, you gain a +2 bonus to attack and damage rolls made with this magic weapon, and attacks with the weapon deal radiant damage instead of bludgeoning damage. An undead creature hit by the weapon takes an extra 1d8 radiant damage.

While you are holding Duskcrusher and its radiant head is active, you can use an action to cast the Sunbeam spell (save DC 15) from the weapon, and this action can't be used again until the next dawn.