Draining Thread

You open a wound on your body, shooting out a thread of blood between yourself and a creature within range. As you cast the spell, you must spend a number of hit points. The creature must then succeed on a Dexterity saving throw or take 4d8 + double the number of hit points spent as necrotic damage on a failed save and half as much on a successful save. If this damage brings the target to 0 hit points, the hit point cost is refunded as blood drains through the thread back into your body.

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 4th.