Green dragon bile
inhaled (toxin) - 2500 gp
This greenish heavy gas is one of the deadliest mass poisons. Fortunately, due to the difficulty to get the basic substance, its price makes it an extremely rare poison.
A creature subjected to this poison must make a DC 22 Constitution saving throw, becoming poisoned for 1 hour and taking 45 (10d8) poison damage on a failed save, or half as much damage on a successful one.
Recueil des poisons d´Tapouweb