Blackblood

Hemomancy HP cost min/max: 1/10
You transform a portion of your blood into a poisonous substance.
As you cast this spell, you must expend a number of hit points. You
gain a number of temporary equal to the amount expended. For as
long as these temporary hit points last, whenever a creature hits you
with an attack while within 5 feet of you they become poisoned for 1
minute. A creature poisoned in this way makes a Constitution saving
throw at the end of each of their turns, ending the effect on a success
or taking 1d6 poison damage on a failure.
At Higher Levels. When you cast this spell using a spell slot of 2nd
level or higher, you gain 1d4 additional temporary hit points for each
slot level above 1st.