Bloody Revenge

After taking damage you bend magic to turn your spilled blood into a weapon.  Any creatures within 5 feet of you when you take damage must make a DEX saving throw, taking 2d8 necrotic damage on a failed save, or half as much damage on a successful one. The save is a DC of 8 + proficiency modifier + CON.
Additionally, you can continue to deal damage with your blood. As an action you can move the spilled blood that is initially centered around you up to 30 feet. The blood can make an attack against a creature with 5 feet of it, causing them to make a DEX save with the same results as before. The spell continues for a minute or until you have dealt damage equal to the damage you were initially dealt as a reaction.

(adjusted version of the spell "Blackened Blood" by Trentsw)