Clouds are temporary dungeon features which occupy tiles. They usually cause damage or status effects to anything which occupies the tiles they are in, though some of them do nothing more than block LOS. They come in a variety of elemental flavors, can be created in many different ways, and can be potent weapons if handled properly. Clouds will dissipate on their own in time, but some areas will perpetually generate new clouds. Regardless of the type of cloud, player-generated clouds cannot be placed outside of LOS and will dissipate faster should the player move away from them.
Clouds of flame are tiles which have caught on fire. They deal fire damage to anything standing in them, and can ignite trees in neighboring tiles. Weak intelligent monsters will avoid walking through them, but strong or mindless monsters will charge through, taking damage each turn. Firing an Ice Magic spell through them will put them out. They can be created with the Conjure Flame spell, the Ignite Poison spell, using a red draconians breath attack, using Trog's Burn Books ability, being a demonspawn with Ignite Blood 3, and by igniting bushes or trees with a powerful Fire Magic spell.
- Damage per turn: 10 + (3d23)/3 to the player; 6 + (3d16)/3 to the monsters (affected by fire resistance)
Freezing clouds are tiles filled with brutally cold mist. They function almost identically to flame clouds, except that the damage they deal is cold and they don't have any effects against trees. They can be created with the Freezing Cloud spell, by using Ice Magic over a body of water, or by destroying a simulacrum. Miscasting some Ice Magic spells can also create clouds of freezing vapour.
- Damage per turn: 10 + (3d23)/3 to the player; 6 + (3d16)/3 to the monsters (affected by cold resistance)
Mephitic clouds are tiles filled with noxious fumes, and are often used by casters to defeat poison-vulnerable enemies; anything caught in one is confused for several turns. The most common sources are the Mephitic Cloud spell and the breath attacks of swamp drakes and green draconians, although they can also be created by some miscasts.
- Damage per turn: 1d3 (poison resistance gives immunity)
Poison clouds are tiles filled with poison gas. Anything caught in one will take damage and be poisoned. For even more damage, use the Ignite Poison spell to immediately convert these into flame clouds. These are generally created by the Poisonous Cloud spell, although some miscasts can also create them. Swamp dragons breathe these, as can player nagas with the appropriate mutation.
- Damage per turn: 1d10 (poison resistance gives immunity)
Steam clouds are tiles full of scaldingly hot mist. These do minor damage, and anything with fire or steam reistance is immune to it. Also, the clouds will block LOS much like fog. Any area that has lava exposed to water will emit an endless amount of steam. You can create steam yourself by using Fire Magic over water, or with a pale draconian's breath attack.
Miasma clouds are extremely dangerous banks of corrupt fog. Anything caught in one will be slowed, poisoned, and rotted. They are extremely useful in combat, so long as you don't get caught in the blast yourself. They can be found in the undead version of Swamp:5, created with the Corpse Rot spell or the Foul Stench demonspawn mutation, and death drakes will breathe them at you.
- Damage per turn: (3d12)/3 (rotting resistance gives complete immunity, poison resistance stops you from being poisoned, and stasis prevents you from being slowed)
Mutagenic clouds are fogs of chaotic energies. Stepping in these clouds will inflict heavy magical contamination upon a player which, if left unchecked, may cause bad mutations. They can also polymorph monsters once per turn the monster spends in the cloud. These clouds are usually only found in vaults.
This goes by a variety of names, such as smoke, fog, mist, or colored fog. All do nothing but look pretty and block LOS. It is naturally found in some areas (e.g. mist in Swamp, smoke near lava, etc), can be created by a scroll of fog or the unrandart Cloak of the Thief, and can appear via miscasts, Xom, and a few other sources. Xom may also cause you to trail colored fog from time to time.
While stepping in these clouds has no effect, blocking LOS can sometimes be a lifesaver, as it will stop most monsters from casting spells at you.