Elisteran's Conflagration

Drawing blood from the Wrentiron rune on your body, you select one target within range, and send a concentrated beam of energy into the target dealing 10d8 fire damage. Instantaneously white hot fire erupts from their mouths in a 20 foot cone in front of them. Every creature in the blast must make a Dexterity Saving throw. On a failed save, each creature takes 3d8 fire damage and is considered on fire. The target can repeat its save at the beginning of each turn, on another fail the creature takes another 3d8, on a success the fire is put out. The original target creature is internally on fire until the spell ends or concentration is broken, taking another 4d8 fire damage each turn