Source: The Book of Many Things

Armor (medium), uncommon

While wearing this armor, you can take a bonus action to make the armor emit poisonous spores, which fill a 10-foot-radius sphere centered on yourself. Each creature in that area must succeed on a DC 15 Constitution saving throw or have the poisoned condition until the end of your next turn. Once this property is used, it can’t be used again until the next dawn.