Vitriolic Missile or Poison Ball is a poisonous projectile usually shot from a wall or other obstacle by the result of triggering a trap. While traveling it leaves a trail of poison cloud behind it. This projectile is similar to a spike ball in being moderately slow moving so it is easy to dodge. The missile itself does only mild physical damage but poison clouds are lethal in large doses at least for the hero's companions.
Vitriolic Missiles are usually seen along with spike balls in the depths of the Kehjistan Jungle where the aboriginal people have booby trapped their sacred statues and monoliths.