Blood Parasite

You infect a creature within range with blood parasites that slowly eat away at it from the inside. At the beginning of each of the infected creature’s turns, it makes a Constitution saving throw. On a failed save, it takes 2d6 necrotic damage and you gain hit points equal to half the damage dealt. On a successful save, the effect ends.

At higher levels: For each spell level above 3rd, increase the damage by 1d6 necrotic damage.