Blackblood

You transform a portion of your own blood into a poisonous substance. As you cast this spell, you must spend a number of hit points. You gain a number of temporary hit points equal to the amount spent. For as long as those temporary hit points, whenever a creature hits you with an attack while within 5 feet of you they take 1d8 Poison damage and become poisoned until the start of their next turn. 

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, you gain 5 additional temporary hit points for each slot above 1st.