|This spell conjures up a large but short-lived cloud of vile fumes.|
Mephitic Cloud is a Level 3 Conjurations-Poison-Air Magic spell that creates up to a 3x3 cloud of noxious fumes which will linger for several turns. It does not affect unbreathing creatures (undead, nonliving, and plants), nor those that are poison resistant.
Any other creature caught in it will take a bit of poison-based damage, with a (21 - hit dice) in 21 chance per turn to become confused, unless the creature has clarity. Monsters with 22 hit dice or more have a flat 98% chance of not being affected.
The clouds stay a duration of 1d (Spell power / 50) turns.
Mephitic Cloud makes as much noise as Fireball.
This spell is found in multiple spell books, including several starter spellbooks. Despite how it can be blocked by two different resistances, it is very useful, even with minimal skill in the relevant magic schools. It is highly effective against most of the most dangerous monsters in the early to mid game, such as centaurs, spellcasting orcs, and yaks.
The confusion effect essentially disables creatures and allows you/your minions/your spells to kill them much more easily. The longer they spend in the cloud, the longer the victims will be confused. Alas, it will not affect undead or other poison-resistant enemies, but those can sometimes be distracted by attacks by their confused neighbors.
If you are poison resistant or are have the clarity intrisic, you can use it anywhere without fear of affecting yourself. If surrounded, you can even target yourself.
Even if you're not poison resistant, Mephitic Cloud can be used against an adjacent enemy in most cases (aim at the *):
......... ......... ...###... ....###.. ...#*#... ....#*#.. ...##Y... ....Y##.. ....@.... ....@.... ......... .........
By targeting diagonally beyond the yak, you can catch it in the cloud radius without catching yourself.
Since Mephitic Cloud can be targeted at an empty square, this increases its effective range by one, allowing you to catch an enemy just beyond its normal range. When facing distant enemies with dangerous ranged attacks (such as centaurs), a good strategy is to drop a cloud between you and them, then back away until they blunder into it.
In 0.10 Mephitic Cloud was changed to no longer guarantee a 3x3 cloud.