Balin's Volatile Eruption

The ground beneath their target begins to rumble. A deep, guttural roar echoes from below, like the earth itself awakening in rage. The soil splits open in jagged cracks glowing molten orange, and a geyser of magma, burning ash, and shrapnel of rock bursts forth in a deafening explosion. Each creature in a 20-foot-radius Sphere centered on that point makes becomes difficult terrain and make a Dexterity saving throw, taking 6d6 Fire damage on a failed save or half as much damage on a successful one. Each creature that starts its turn within the 20-foot-radius takes 2d6 Fire damage.