When you use a weapon's Explode property, you can fire a Clusterbomb. The explosion is a 20-foot-radius Sphere. On a failed save, a creature takes 10d6 Fire damage, or half as much damage on a successful save. This damage ignores Resistance. A Huge or smaller creature that takes damage from the Clusterbomb has the Prone condition.
Once you use this feature, you can't use it again until you finish a Short or Long Rest. You can also restore your use of it by expending four Risk Dice (no action required).