Rod of clouds
Evoking a rod of clouds casts Cloud Cone, filling a cone-shaped area in front of you with one of several randomly selected cloud types. At low evocations skill, this rod frequently conjures simple, harmless mist, but it can occasionally produce damaging clouds as well. With high skill, its random nature can still make it useless (conjuring negative energy against undead), but it can be also be devastating (poison against insects, thunderstorms against most creatures, acid against almost anything.)
The long duration of summoned clouds typically means that you'll need to move if you want to try for a different effect against a given set of creatures, as the fight is likely to long since be over by the time the air is clear.
Even with a low evocations skill, this item can be quite useful, particularly in the early- and mid-game when many more monsters will be susceptible to its effects. It comes in most handy for crowd control, particularly as a group of monsters first reaches you (i.e. before you are surrounded) and at chokepoints. It only takes an evocations skill of 3 or more to begin seeing freezing clouds and poison gas. Even before this, noxious clouds of confusion will occur often and cause vulnerable monsters to hit their compatriots in their confusion. All it requires is poison resistance, and you can enter these clouds safely and add to the fray. Even the unfortunate expulsion of rain clouds can create shallow water that non-large monsters will splash around in.
The downside of this item is that is creates much hunger. Its use should be curtailed if one does not have ample access to foodstuffs or consumable corpses.