Lavaburst Caltrops

Hot Feet. As an action, you can spread this bag of caltrops to cover a 5ft. square area. A creature that enters the area activates the caltrops, causing an explosion of molten rocks to erupt from the caltrops. The creature must make a Dexterity saving throw (DC 17). On a failed save they stop moving and take 8d6 Fire damage. On a successful save they take half damage and can still move. A creature moving through the area at half speed makes the saving throw with advantage.   After activation, the caltrops are destroyed and the molten rock turns the ground within 5ft. of where the caltrops were scattered into difficult terrain for 1 minute. When a creature starts their turn in the area or whenever it enters it for the first time on their turn, they have to make a Dexterity saving throw (DC 17). On a failed save they take 4d6 Fire damage. On a successful save they take half damage.