Enervation

A tendril of inky darkness reaches out from you to drain life from a creature you can see within range. The target makes a Dexterity saving throw. On a failed save, the target takes 6d8 Necrotic damage. On each of your subsequent turns, you can take a Bonus Action to deal 2d8 Necrotic damage to the target automatically. The spell ends if the target is ever outside the spell's range or it has Total Cover from you. On a successful save, the target takes half the initial damage only, and the spell ends. Whenever this spell deals damage to a target, you regain Hit Points equal to half the amount of Necrotic damage dealt.

Using a Higher-Level Spell Slot: The initial damage increases by 1d8 for each spell slot level above 5.