Blood Sacrifice

You point at a creature of your choosing within range. You then take 60 Necrotic damage, that cannot be reduced in any way, and the chosen creature receives double the Necrotic damage you take as healing. 

Your maximum hit points are also reduced by 20. This reduction to your maximum hit points cannot be avoided by any means. This wears off after a long rest.
Should this spell reduce your maximum hit points to 0, you are instantly killed.

At Higher Levels. When you cast this spell using a spell slot of 8th level or higher, the Necrotic damage that you take increases by 20 and the maximum hit point reduction increases by 5 for each level above 7th.