The Shattered Mountain Weeps

A massive sphere of rock explodes, unleashing a cataclysm of falling debris and deadly shrapnel. Its destruction falls in a 20-foot area within 120 feet. Creatures in the area take scaling d10 bludgeoning damage with a fortitude save against your class DC. Those who fail are knocked Prone. For the next minute, rocks continue to fall, making the area difficult terrain and dealing scaling d10 bludgeoning damage to any creature that ends its turn in the area. If you use this impulse again, any previous one ends.

Level (20th) The initial damage is 10d10, and the area damage is 4d10.