Symbiote’s Retribution

when damaged by a melee attack, your body sends back black ooze that stabs through the attacker. The creature must make a Dexterity saving throw. It takes 2d10 necrotic damage on a failed save, or half as much damage on a successful one. On a failed save, it also leaves the target vulnerable for one round to all damage 

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the damage increases by 1d10 for each slot level above 1st.