As part of casting this spell, you must expend four Hit Point Dice or the spell automatically fails. Make a melee spell attack against a creature within 5 feet using the Material component of this spell. On a hit, roll the Hit Point Dice expended to cast the spell plus 4d8. You deal Necrotic damage equal to the roll's total. If this damage causes the creature to be reduced to 0 Hit Points, it immediately dies and you gain one of the following dark blessings of your choice.

Unassailable. You have Advantage on all saving throws you are proficient at.

Unbreakable. Your size increases by one category (from Medium to Large, for example), you gain a number of Temporary Hit Points equal to your Constitution modifier (minimum 1) at the start of each of your turns, and your weapon attacks deal an extra 1d4 damage.

Unerring. Your Proficiency Bonus increases by 1.

Your dark blessing ends after 10 minutes or when you are reduced to 0 Hit Points, whichever happens first.

When you take Radiant damage while you have a dark blessing, you take an extra 1d4 Radiant damage.

AN: Might be too edgy even for DK and might be just about totally unbalancabled with these blessings. Unassaiable nerfed from all saving throws to only those you are proficient at (Might need even bigger adjustment). Unerring nerfed from 2 to 1. Also heavily adjusted components to match this clearly dark spell.

AN2: Might want to even adjust the name. This doesn't roll well over the tongue.