Blood Blight

You offer up half of your maximum hit points to place a curse on an enemy you can see within range.

The target must succeed on a constitution saving throw, or be marked by your curse. On a failure, the target takes necrotic damage equal to one of your hit dice plus your spell-casting modifier, and then every round at the start of its turn. Every round, at the start of it's turn, the target takes twice as much dice damage up to a maximum of 4. The Target repeats its saving throw at the end of its turn, ending the spell on a success. 

If a target dies as a result of the damage dealt by this spell, you add the amount of damage dealt to your hit point maximum and current hit points and the spell ends. Your hitpoint maximum is restored to normal after a short or long rest, or by using Greater restoration or similar magic.

At Higher Levels. For every 2 spell levels above 5th, the maximum damage is doubled. At 7th level, your hit dice damage maximum is 8 hit dice, and at 9th level the maximum is 16 hit dice