Erupting Blood

You target a creature sympathetically through a drop of their blood you have recently collected. As the spell takes effect they feel their blood boil as it tries to reopen the previous injury. The target makes and Intelligence saving throw, on a failed save the target takes 3d6 necrotic damage (lowering their hit point maximum by half that number) and suffers one level of exhaustion. On a save the target takes half the necrotic damage and does not lower their hit point maximum or suffer exhaustion. If a lesser restoration or remove curse (or higher spell) is used on the target, the hit point maximum reduction and exaustion conditions are both ended immediately.

If the same creature is targeted and fails the saving throw more than once, it does not suffer additional levels of exhaustion and only lowers it's hit point maximum once (if a higher damage roll occurs later use the highest number to lower the hit points only)

At Higher Levels: When you use a spell slot of 5th level or higher you increase the necrotic damage by 1d6 for each spell slot above 4th. For every 2 spell slots above 4th the target also suffers an additional level of exhaustion on a fail (2 levels using a 6th level spell slot, 3 on an 8th)