Burning Blood

You fling blood from an open wound into a point within range, coating a 15-foot radius sphere in arcane charged ichor for 1 minute. Any creature within the area must make a dexterity saving throw or be marked with blood. 

Once, as a bonus action during the spell's duration, you may activate the blood to ignite and explode into pinkish flames. Unmarked creatures inside the coated area must make a dexterity saving throw. A target takes 3d6 fire and 3d6 necrotic damage on a failed save, or half as much damage on a successful one. Marked creatures fail this save automatically.