You ignite your steps with blazing flames. Until the end of the turn, your speed increases by 20 feet, and you leave behind a burning surface in a 5-foot wide line following the path you move. The burning surface is difficult terrain, and each creature that enters the burning area for the first time on a turn or starts their turn inside it must make a Dexterity saving throw. A target takes 4d6 fire damage on a failed save, or half as much damage on a successful one.   The flames in the burning area last for 1 minute or until it is cleared by some environmental effect, such as a wave of water or a very strong gust of wind.