You fling a supercooled piece of magnetite at a point you can see within range, where it detonates in an explosion of icy, metallic shards. Each creature in a 20-foot-radius sphere centred on that point must make a Dexterity saving throw, taking 4d6 cold damage and 3d6 piercing damage on a failure, or half as much damage on a success. Creatures made of a ferrous material or wearing ferrous armour have disadvantage on this saving throw.