Eldritch Death Touch

You touch a creature. Make a melee spell attack roll. If it hits creature makes Constitution saving throw. If it fails it is reduced to 0 hit points, dies and you regain hit points equal to half the damage dealt. If it succeeds it takes 15d10 necrotic damage. If this damage reduces it to 0 hit points it dies. You regain hit points equal to half the necrotic damage dealt.