Poison Armor of Amphibios (Patreon)

Armor (any light armor), rare (requires attunement)

This armor is enriched by poisonous frog toxins. While wearing this armor, you have advantage on saving throws against poison, and you have resistance to poison damage. In addition, the armor has 3 charges and regains all expended charges daily at dawn. When a creature within 5 feet of you hits you with a melee attack, you can use your reaction to expend 1 of the armor's charges to release a spray of poison from the armor at the attacker. The attacker must make a DC 15 Constitution saving throw. On a failed save, the target takes 2d6 poison damage and is poisoned until the end of its next turn. On a successful save, the target takes half as much poison damage and isn't poisoned.

"Now, now, don't bite me. I promise I taste awful."