Collateral Spell Effects (POSM)

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Everyone knows that a fireball does 1d6 damage per level of the caster, but have you ever stopped to consider what else a ball of flame 40 feet across might do? First of all, a fireball will start a lot of fires, especially in medieval settings with thatch-roofed houses, garments redolent with animal oils and tanning chemicals, and lots of wooden construction. Secondly, the residual fires left by a fireball will produce smoke—probably a lot of it, as many fires smoke very heavily just when they're getting started. Next, a fireball may foul the air of a confined space by consuming a great amount of the available oxygen. But, for most players and DMs, the same fireball did 17 points of damage, and that was it!
In this section, we'll take a quick look at unusual effects that may accompany the use of many powerful spells. In military terms, these incidental effects are referred to as collateral damage—a PC wizard probably isn't trying to start a three-alarm fire when he torches a city guard with his burning hands spell, but it might happen anyway. Depending on the DM's mischievousness, all kinds of mayhem may break loose when wizards start throwing heavy-damage spells around.
The most important characteristic of a spell for purposes of collateral effects is its general type and purpose. There isn't a whole lot of fallout from a charm person or magic missile spell, but many other spells create environmental effects that may be long-lasting or even permanent.
==Fire==
A great number of spells employ fire as a weapon. Fires create smoke, foul contained atmospheres, and may spread to nearby flammables.
Visibility: Flames don't produce smoke—burning objects or creatures do. A fireball thrown in an unfurnished room of bare stone against a creature that won't burn well (say, an ice elemental) will leave very little in the way of heavy smoke. On the other hand, a fireball thrown in a sod house or a wooden building cluttered with greasy old furs and shoddy furniture will create a number of smoky residual fires and quickly cloud up the surroundings. Generally, a fire spell creates a cloud of smoke in its area of effect that persists for 2d4 rounds. This obscures vision, forcing all characters and monsters to suffer a –2 penalty on missile attacks through the smoke. The stink of burning objects may also hinder creatures that rely on scent to detect their enemies.
Environmental Effects: Fire spells naturally cause fires. See Item Saving Throws on page 58 of the DMG . In addition to the affected characters, the DM can roll an item saving throw for the surrounding area; for example, if a stone room is furnished with tapestries and wooden benches, the DM can use the row for cloth and thin wood.
If an item (or a victim's clothing, for example!) fails its saving throw, it may be on fire. People who catch fire suffer 1d4 points of damage in the following round and an additional die of damage in each subsequent round—for example 2d4 in the second round, 3d4 in the third round, and so on—until they extinguish the flames. The victim must pass a saving throw vs. death magic in order to extinguish the flames and may gain a +2 to +8 bonus (DM's discretion) if he uses a sensible method for doing so.
Large fires in confined areas (for example, dungeon rooms) can be especially dangerous since they deplete the oxygen in the air, making it unfit for breathing. If a fire fills more than 50% of an enclosed room or space, it fouls the air. Air-breathing creatures inside the room are affected as if the entire chamber had been targeted with a stinking cloud spell. After 1d6 rounds of ventilation (or 1d6 hours in an unventilated area), the atmosphere returns to normal.
One more thing about big fires: they make things hot. Imagine a character's surprise when he goes to open the castle gates just after the wizard's fireball goes off! In fact, the DM may rule that metal and stone objects retain enough heat to be affected as if they were struck with a heat metal spell, although under most circumstances they will only be heated to the minimal damage level of the spell.
==Cold==
Cold-based attacks are rarer than fire-based attacks but are still fairly common among wizard spells. The most obvious examples are ice storm, cone of cold, and Otiluke's freezing sphere.
Visibility: The supernatural temperatures of a cold-based spell can cause some surprisingly thick fog by condensing water vapor in the air. The more humid the setting, the more likely it is for cold-based attacks to leave a residue of fog. Generally, cold spells create a cloud of fog equal in size to the spell's area of effect. The fog persists for 1d6 rounds, and any attacks in or through the mist suffer a –2 attack penalty.
Environmental Effects: Cold spells don't start fires, but they can leave a dangerous coating of ice on the ground; in fact, the ice storm spell specializes in this effect. Creatures moving in the area of effect have a 25% chance of risking a slip or fall, which a saving throw vs. death magic (or a Dexterity check, DM's choice) can avert. Note that this is not as dangerous as the sleet application of ice storm since that version of the spell is designed to coat the ground with slippery ice.
Objects subjected to intense cold may be weakened or become unusually brittle for a short time afterwards. Even if an item passes the saving throw, for the next 1d6 rounds it is especially vulnerable to normal blows or crushing blows, suffering a –4 penalty on any further item saving throws.
As noted under fires, metal or stone objects subjected to supernaturally cold temperatures may be affected as if struck by a chill metal spell.
==Electricity and Lightning==
The distinction between lightning and electricity is principally one of hitting power. A lightning bolt's immense voltage allows it to overcome the resistance of many things that normally don't conduct electricity at all. In addition, the power of a lightning bolt is so great that the target can blow itself to pieces as its fluids or water content is flashed to steam and then expands. This is why trees hit by lightning bolts split open; the water in the wood bursts the tree from inside as it turns to steam.
In the AD&D magic system, lightning bolt, call lightning, chain lightning and blue dragon breath are lightning attacks. Shocking grasp, glyphs of warding, and the touch of a volt, shocker, or electric eel are electricity attacks.
Visibility: The bright arc of electricity or the flash of lightning as it strikes can temporarily dazzle people looking right at the bolt or spark, especially when the viewers' eyes are adjusted to darkness or dim light. In this case, the DM may require onlookers to make a saving throw vs. death magic or suffer a –1 attack penalty for 1d3 rounds as their vision clears.
In addition, lightning and electricity may start fires if applied to flammable targets (wood or trees usually, but not people). The smoke from a lightning-struck fire can be just as disorienting as the smoke from a fireball.
Environmental Effects: Lightning and electricity leave few lingering effects behind; a stink of ozone (ionized air) may persist for 1d6 rounds, possibly confusing creatures that rely on smell to detect their prey, and objects may be magnetized by their exposure to powerful electrical currents. This is not fantasy magnetism capable of picking up an armored warrior and hurling him through the air; this is low-level magnetism capable of skewing compass needles and lodestones.
Flammable items that fail their saving throw vs. lightning or electricity must make a second saving throw vs. normal fire or begin to burn. This may in turn cause smoke and other such effects.
Lightning bolts cast underwater electrocute everything within a 20-foot radius of the bolt's origin. Since the wizard can start the bolt up to 40 feet away from his position, he would be wise to do so when using this spell in an aquatic setting. If a caster out of the water throws a lightning bolt into the water, the bolt has its normal effect on any creature in its path until it strikes the surface of the water; at that point, it expands in a 20-foot-radius globe in the water, and goes no further.
==Acid==
Another unusual attack form is acid. Very few spells make use of acid as a weapon, although a fair number of monsters have acid-based attacks, including the ankheg, the black dragon, and some slimes, puddings, and oozes.
Visibility: Acid at work tends to give off noxious fumes, usually in an area about 5 to 15 feet in diameter; the more acid, the larger the area affected. The fumes may obscure missile and melee attacks at the DM's option, creating a –1 penalty for any creature trying to attack through the smoke and haze.
Environmental Effects: Acid fumes are unpleasant to be around and may cause severe irritation of a victim's eyes, nose, and throat. If the DM desires, creatures within the cloud of fumes must roll saving throws vs. death magic or suffer a –2 penalty to attack rolls and Armor Class as long as they remain nearby. This means that a character struck by Melf's acid arrow may suffer combat penalties as well as damage from the spell.
==Wind==
Spells or effects that generate powerful gusts of wind can create a number of collateral effects. Enchantments such as dust devil, gust of wind, wind wall, and control wind are the most common in this group, and monsters such as djinni or aerial servants can create whirlwinds.
Visibility: While a blast of wind doesn't necessarily obscure visibility, a gust on a very dusty or sandy surface is a different story altogether. On a dry, gritty surface, a wind-based spell or attack will create a rolling dust cloud that creates a –2 penalty for people trying to fight or fire missiles into or through the area of effect.
A blast of wind can also make it very difficult to hear anything above the roaring of the air and may carry a character's scent downwind and away from a creature that relies on smell or hearing to locate its enemies.
Environmental Effects: Strong winds can create all kinds of havoc in a dungeon by extinguishing torches and candles and plunging the party into darkness. Above the ground, it can carry the sparks from a campfire farther than normal or blow over a lamp, possibly starting an unexpected fire.
==Other Collateral Effects==
Magic is astonishing and almost always has effects or uses that are not immediately apparent. Feel free to improvise when a player in your campaign tries something that seems especially clever—or stupid. What happens when a purple worm is polymorphed into a puppy dog just after swallowing a still-living character? Or how do the various rays of the prismatic spray affect the area around them if they miss their target? What kind of wreckage does an acid storm spell leave behind when cast in a forest clearing? Be creative and take your best guess; the AD&D game is made of exceptions and special cases.