Black Blood

When you cast this spell, your current hit points are reduced by an amount equal to the spell's level.

You toxify your own blood, turning it into a weapon when your enemies harm you. When a creature hits you with a melee attack, the creature takes 1d10 necrotic damage.

If the attack is a bite attack, the creature takes an additional amount of necrotic damage equal to your spellcasting modifier, and none of the necrotic damage inflicted by this spell can be reduced or prevented in any way. If the creature would normally regain hit points as part of the attack (such as the bite attack of a vampire), the creature does not regain any hit points. In addition, the attacking creature must succeed on a Constitution saving throw or be poisoned for 1 minute, even if it is normally immune to the poisoned condition. The creature may repeat the saving throw at the end of each of it's turns, ending this effect on a success.