Venomous Retaliation

When a creature within 5 feet of you hits you with a melee attack, you can use your reaction to lash out with shadowy tendrils that erupt from you. The attacker must make a Constitution saving throw (DC = 8 + your [ability]Dexterity[/ability] modifier + your proficiency bonus) or take 2d10 poison damage and become poisoned until the end of their next turn. This feature can be used once per long rest.