Cymbeline

Choose a point you can see on the ground within range. Fissures open in the ground as lava and earth spikes erupts in a 40-foot cube centered on that point. Each creature in that area must make a Dexterity saving throw. A creature takes 4d12 magical bludgeoning damage and 7d10 fire damage and is knocked prone on a failed save, or half as much damage on a successful one.

Additionally, the ground in that area becomes difficult terrain until cleared, and any character that ends its turn within the cube, takes damage equal to your spell-casting modifier in fire damage. Each 5-foot-square portion of the area requires at least 1 minute to clear by hand.

This spell was created by Cameron the Clairvoyant. While adventuring in the multiverse, he ended up on the continent of Tellius, in the Empire of Begnion. There he spent time interacting with the Greil Mercenaries, and as an advisor to the Phoenix Empress Sanaki of Begnion. Later in their adventure, Cameron witnesses the true power of Empress Sanaki, for with this spell, she decimated an entire army of heavy-armor knights.