The Noxious Potion is a potion that releases green clouds of smoke when completed. It's exact usage and effects are unknown, but it is possible that it is used as a poison.
Etymology
In Latin, "Noxious" means unpleasent and harmful, generally refering to odorous fumes, hence the green clouds that emit from it. Noxious is a desendant of another Latin word, nocere, meaning to hurt or injure. "Noxa" means hurtful or injurious. This means that the potion possibly injures the drinker.