A Poison Mist is a mist monster that is encountered during the Shadows of Amn campaign.
They are summoned by Barl inside the Temple of Waukeen located in Trademeet if he is attacked during the Save Mazzy's Sister, Pala side quest. They will spawn in the Slime laboratory when the Guardian of Air is defeated in the Air laboratory, located on the Watcher's Keep Elemental Level.
They may also randomly spawn in locations where other mist monsters such as Vampiric Mist, Crimson Death, and Mist Horror are encountered.
Poison Mists are immune to acid and poison damage. They have 25% resistance to all forms of Physical damage and are immune to non-magical weapons.
A Poison Mist's only weapon is a 1d2 slashing damage attack delivered by their elongated tentacle-like fingers. A successful hit inflicts 1d10 Poison damage, with the additional hazard of causing a Poison status effect. The victim of this mist's melee attack must achieve a Saving throw versus Death with a -2 penalty or suffer 2 points of Poison damage per second for 5 seconds.