Vitality Transfer

You touch a living creature. The creature heals for 1d4 hp. You take 1d6 necrotic damage. This damage cannot be mitigated. This spell has no effect on undead or constructs. The target heals for an additional d4 when you reach 6th, 12th and 18th level.

Fluid Vitality: This spell deals 1 additional necrotic damage to the caster for every time they have used this spell or it has been used on them since their last short/long rest.