You transform a portion of your blood into a toxic substance. When you cast this spell, you must expend a number of hit dice equal to the spell slot you used to cast the spell. A coat of black liquid surrounds you. You immediately roll the hit dice and gain a number of temporary hit points equal to the number you rolled.   For as long as these temporary hit points last, every time a creature hits you with a melee attack must make a Constitution saving throw or 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 success or taking 1d6 poison damage on a failure.