Heart of the Fires

Wonderous Item - Legendary
This heavy cluster of crystal, stone and bone is engraved with hundreds of Abyssal runes, and is permanantely hot to the touch. Over the course of a day, it builds in heat and mass, growing heavy and unpredictable in weight, burning and shuddering and vibrating until it's released.
The Heart can be thrown a distance equal to the wielder's Strength (Athletics) check. Upon landing, each creature within 20 feet of the Heart is hit by a wave of intense heat.
Roll 10d10 fire damage. The amount rolled is split evenly between all creatures within 20 feet of the Heart. A creature may make a DC15 Constitution save to halve this damage.