Dundragon's Wave of Rolling Earth

You strike the ground in front of you and command it to roll and turn. Each creature on the ground in a 25 foot cube originating from you must make a Dexterity saving throw. A creature that fails the save takes 4d12 bludgeoning damage and is knocked prone. A creature that succeeds the save takes half as much damage and isn't knocked prone. If the ground in that area is loose earth or stone, it becomes difficult terrain until cleared, with each 5-foot-diameter portion requiring at least 1 minute to clear by hand.