Comet Ballista

This crossbow is partially covered in cold shards of stone and metal and uses sling bullets as ammunition instead of crossbow bolts. When you fire a sling bullet from this magic crossbow, it flashes with blue light and leaves behind a brief, glimmering trail of cold, sparkling dust. Ranged attacks with this weapon deal bludgeoning damage, instead of piercing damage, and any target hit by it takes an extra 1d6 cold damage. In addition, the first time you hit a target on each of your turns with a ranged attack using this weapon, each creature within 10 feet of the target must succeed on a DC 13 Constitution saving throw or take 1d6 cold damage.

Hailing Comets. You can use an action to fire the crossbow into the air and speak its command word, choosing a point that you can see within 120 feet of you when you do. The sling bullet scatters into icy dust and is destroyed, but magically conjures a barrage of miniscule falling comets above the point. The comets fall in a 20-foot-radius, 40-foot-tall cylinder centered on that point and disappear once they hit the ground. Each creature within the area must make a DC 13 Dexterity saving throw, taking 8d6 cold damage on a failed save, or half as much damage on a successful one. Once this property has been used, it can't be used again until the next dawn.