Source: Guildmaster's Guide to Ravnica

Wondrous item, rare

This short tube, about 2 feet long and 6 inches in diameter, is made from mizzium, a magically enhanced metal alloy forged by the lzzet League. The end that's pointed toward a target is open, and a glowing ball of molten metal can be seen at the other end as long as the mortar has at least 1 charge remaining.

The mortar has 4 charges for the following properties. It regains ld4 expended charges daily at dawn.

Molten Spray. You can expend 1 charge as an action to loose a 30-foot cone of molten mizzium. Each creature in the area must make a DC 15 Dexterity saving throw, taking 5d4 fire damage on a failed save, or half as much damage on a successful one.

Mizzium Bombared. You can expend 3 charges as an action to launch a hail of molten projectiles in a 20-foot-radius, 40-foot-high cylinder centered on a point you can see within 60 feet of you. Each creature in the area must make a DC 15 Dexterity saving throw. A creature takes 5d8 fire damage on a failed save, or half as much damage on a successful one.