Xotec's Siphon Life

A black mist of ethereal darkness appears around a creature you can see within range to siphon the life from it. The target must make a Constitution saving throw. On a failed save, the target takes 5d8 necrotic damage and its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if its hit point maximum is reduced to 0. On a successful save, the target takes half as much damage and its hit point maximum isn't reduced. This spell has no effect on constructs.

Whenever the spell deals damage to a target, you regain hit points equal to half the amount of necrotic damage the target takes.

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, the damage increases by 1d8 for each slot level above 5th.