The following is an array of magical and perplexing mists,fogs,cloud,smoke and vapors with which to dress up your fantasy campaigns.
Mist Traps and Sudden Mists fill a 10'-40' radius typically but slowly rolling mists expanding into an area even if relatively harmless add a degree of drama. Most mists are dense enough to limit vision to 20' or less within their boundaries, missile fire through an area obscured by mist should provide significant penalty to attackers success.
Mists Table (1d100)
1-2- Lycanthrope Fog: swirling foggy mist, heavier near the ground. Occupants that fail a save vs breath weapons will be transformed into lycanthropes (of type determined by ref)for as long as they stay within the mist and 80% of the time for up to 7-12 turns after leaving the mist, 20% of the time victims will instead be infected with normal lycanthropy afterward.
3-5- Healing Mist: Anyone exposed to this mist will recover 2-7 hp of damage of wounded at the time of exposure. This mist will only benefit a being once per day.
6- Midas Mist: anyone in mist must pass a save every 2 rounds or their person and all equipment carried is turned into gold (living beings will be immobile as when turned to stone). Equipment thrown into the mist doesn't turn into gold if it isn't carried by living being.
7-10- Purple Haze: Anyone exposed to this mist that fails a save will hallucinate and on a second failed save they will turn to stone.
11-20- Acid Vapor: The mists is a a cloud of acid...arg!!! The mist will do 1d6 damage per dungeon level, successful save will halve the damage.
21-25- Tear Gas: This mist overcomes victims who will cough and be overcome with tears for 1-4 rounds after exposure.
26-30- Choking Cloud: A failed save overcomes a victim who suffers 1d3 damage a round in the mist. A save is allowed each round. If three saves in a row fail the victim will be overcome and helpless within the mist and will take damage each round with no save.
31-35- Feeble Vapor: this mist will cause the victim to have their strength reduced to 1/2 normal. Monsters without scores will attack at 1/2 HD and inflict 1/2 damage. Those suffering from the feeble vapor will continue to suffer for 7-12 full turns.
36-40- Rusting Fumes: metals will magically rust on second and following rounds of exposure.
41-60- Dense Fog: vision is reduced to but 10' within the mist even to those with special forms of vision.
61-70-Fog Beast: as dense fog above plus a monster will occupy the mist that may not be harmed by attacks launched from outside the fog.
71-75- Soporific Cloud: anyone failing a save in this cloud will fall asleep for 7-12 hours. Normal means will not wake them.
76-80- Luminous Green Mist: anyone passing through the cloud will glow with a green light for 3 full turns afterward.
81-90- Explosive Fumes: This mist will smell slightly of rotten eggs, any open flames will cause the cloud to explode inflicting 2d6 damage of fiery carnage per dungeon level to all within (dissipating the gas for a hour if a constant hazard).
91-95- Spooky Mist: this oddly clinging and swirling mist is harmless but any undead within may not be turned.
96-97- Phantom Fog: this swirling and shifting cloud of fog will sport the occasional fearsome face and spectral form. Those of 3rd level or less must make a morale save to enter or operate effectively inside a mist. Undead within may not be turned.
98- Ghastly Vapors: These vapors appear to be a spooky mist or phantom fog but anyone lingering in this mist for more then a round must save vs death or lose an energy level. Anyone who dies in these vapors will be lost as will all gear they carried.
Undead within may not be turned and will recover 2 hp a round if harmed.
99-100- Fog of War: all within who fail a save will strike violently at anyone within reach. Those leaving the mist will attack the nearest beiung for 1d4 rounds.
A ref is encouraged to come up with a variety of smells and colors to aid and confuse players attempting to identify a mist without entering it.