Draconic Eruption

Once per long rest, you slam this weapon into the ground. the ground breaks and shatters as lava bursts in a 30 ft. cone in front of you. All creatures within the cone must make a dexterity saving throw with a DC of 18. If they fail, they take 3d8 fire damage and fall prone. If they succeed, they must use their movement to move to the closest space outside the cone.