Envenomed Shield

An invisible barrier of magical force appears to protect you and potentially poison your attacker. Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack. Additionally, if a melee attack misses because of this AC bonus, the attacker must make a Constitution saving throw. On a failed save, the target takes 1d6 poison damage and is poisoned until the end of their next turn.