Blood Armor

3rd-level necromancy

Casting Time: 1 bonus action
Range: Self
Components: V, S (you must have just struck a foe with a melee weapon)
Duration: 1 hour

When you strike a foe with a melee weapon attack, you can immediately cast blood armor as a bonus action. The foe you struck must contain blood; targets that don't bleed don't satisfy the requirement for blood armor. The blood flowing from your foe magically increases in volume and forms a suit of armor around you, granting you armor class 18 + your Dexterity modifer for the spell’s duration. Blood armor has no Strength requirement, doesn't hinder spellcasting, and doesn't incur disadvantage on Dexterity (Stealth) checks.

If the creature you struck was celestial, blood armor also grants you advantage on Charisma saving throws.