Blood boil

You punish tbose who dare attack those under your protection. When a party member takes damage you cause the one who did it to wither in pain as you heat there blood. It makes a constitution saving throw, taking 2d10 necrotic damage on a failed save or half as much damage on a successful one. This spell can only be used on a creature that has some form of blood.

Using a Higher-Level Spell Slot. The damage increases by 1d10 for each spell slot level above 1.