Blood Mist

You put the blood in the palm of your hand, and blow on it. A mist of blood flies forward in a 15 by 5 ft. line, which stays for 2 rounds. Anything that has been in the mist for 3 turns must succeed a Constitution saving throw, or take damage equal to a quarter of their health rounded down

This spell's damage increases when you reach 8th level (a third of health), and 15th level (half health)