if not using Sangromancy this spell is a Transmutation school
Casting Time: Action , Range: 120 Feet , Components: V (Vocal) - S (Somatic) - M (Material) , Duration: up to 1 minuet (Concentration)
Special Material: the skull of a humanoid encrusted in gems worth at least 200 gp
Effect
As part of casting this spell you must expend five hit dice or the spell automatically fails. When you do, choose an aberration, celestial, elemental, fey, or fiend within range and condemn it to a taste of mortality. The creature must succeed on a Charisma saving throw or have its current and maximum hit points reduced. Roll the hit dice expended to cast this spell to determine the amount the creature’s current and maximum hit points are reduced by.
Additionally, for the duration of the spell, a creature that fails the saving throw loses all damage immunities and resistances, its creature type changes to humanoid, and takes an additional 1d4 necrotic damage each time it takes damage.
If a creature affected by this spell is reduced to 0 hit points, these changes become permanent and the creature dies. This final effect of the spell can only be reversed if the creature is restored to life and targeted by a remove curse spell or similar magic.
At Higher Levels
Lore, some nice lore flavour and/or history