More About Adjudicating Illusions (CWH)

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Whether an NPC is able to disbelieve a PC wizard's illusion or whether a PC is able to disbelieve an NPC illusion is ultimately up to the DM. The DM should allow a saving throw against an illusion if the subject has any reason at all to doubt the existence of what he is experiencing. To account for the degree of realism in a given illusion, as well as any information available to the subject about the perceived illusion, the DM should modify the subject's saving throws with appropriate bonuses and penalties.
How does a DM make these decisions? There are a number of factors that can be considered to help determine bonuses and penalties for saving throws. It's unrealistic to expect the DM to meticulously evaluate every aspect of an illusion before he decides on the modifiers, but the following can be used as general guidelines 
==Complexity—Non-Living Objects==
The most important element in determining an illusion's believability is its complexity. The more complex the illusion, the more difficult it is for the caster to get all the details right, and the more likely it is for a subject to notice a mistake. There are more details to a fire-breathing dragon than there are to a stationary boulder, so it is no surprise that a subject would be more likely to disbelieve the illusionary dragon than he would the illusionary rock.
An illusion can be a re-creation of a non-living (inanimate) or a living (animate) object. These need to be treated in different ways.
In general, the complexity of non-living objects depends on size (a pebble vs. a boulder), number (a single boulder vs. a dozen boulders scattered over an area), and appearance (a smooth gray boulder vs. a sparkling, multi-colored gem). External forces affecting the object also affect its complexity (wind blowing pebbles along the ground or an avalanche of boulders tumbling down a hill).
If the illusion has an excessive number of sensory elements, the subject's saving throw may receive a positive modifier. What constitutes an excessive number of elements? A single color or texture (for instance, a smooth gray boulder) is not excessive.  Multiple colors and textures (a pile of various types of gems or minerals) or several different sensory elements (a field of variously colored flowers that have a variety of fragrances) could be considered excessive, as could the illusion of motion, such as boulders tumbling down a hill.
These factors are not necessarily cumulative; in fact, only in the most exceptional cases would an illusion of non-living objects result in a saving throw modifier of more than +2.
Examples:
* An illusion of a single blue diamond. Saving throw modifier: 0. Nothing about this illusion is particularly difficult since it is a single, stationary item.
* An illusion of ten thousand sparkling blue diamonds tumbling in an avalanche down a hillside. Saving throw: +2. There are a large number of items, they're sparkling, and they're in motion. The comparatively high saving throw bonus is also justified by the extremely unusual effect—a character might accept an avalanche of boulders, but an avalanche of diamonds is likely to arouse suspicion.
==Complexity—Living Objects==
Generally, the higher the Hit Dice or level of the illusionary creature, the more complex it is to convincingly create and the more likely it is for a subject to disbelieve. An illusion of an ant is easier to create than the illusion of a dragon. This also applies to illusionary NPCs—a 15th-level warrior is harder to create than a peasant with 3 hit points. Similarly, the more creatures included in the illusion, the harder it is to create; an illusion of 20 peasants would be more difficult than a single peasant.
Illusions of active creatures are more difficult to create than illusions of relatively inactive creatures. If the illusionary creature is executing a simple action, such as standing still, polishing its sword, or grazing in the grass, no special modifier for the subject's saving throw may be required. However, if the illusionary creature is executing a complex series of actions, such as singing a song while dancing and juggling, or attacking with two weapons while shouting a war cry, a modifier may be in order.
If the illusionary creature is a generic monster or NPC—that is, it is a "typical" orc or NPC warrior—there is no need for a special modifier for the subject's saving throw. However, if the illusionary creature is a specific, one-of-a-kind monster or NPC that the subject is familiar with—such as a friend of the subject, or the subject's pet dog—the subject should receive a special modifier.
As with the modifiers for inanimate objects, these factors are not necessarily cumulative. Only in exceptional cases would an illusion result in a saving throw modifier of more than +3.
Examples:
* An illusion of a single orc standing still, polishing his sword. Saving throw modifier: 0. Nothing is particularly difficult about creating an illusion of a single, low HD creature engaged in a relatively simple action.
* An illusion of King Sluz, the famous orc ruler, brandishing his five-pronged trident, screeching a war cry, and leading a squad of six snarling orc soldiers. Saving throw modifier: +3. The modifier assumes the subject is familiar with King Sluz. Casting a believable illusion of a well-known NPC is always extremely difficult, particularly when he is executing a complex action and is accompanied by other creatures.
==Magical Effects and Special Attacks==
Magic is common in most AD&D® campaign worlds, so opponents are not necessarily suspicious of extraordinary effects that appear to defy natural laws.  However, in certain instances, illusions that incorporate magical effects or special attacks will require saving throw modifiers. In general, a wizard cannot create excessively bizarre magical effects in his illusion without arousing the suspicion of the subject, adding a saving throw modifier of as much as +2.
Example:
* An illusion of a pile of sticks that abruptly bursts into flames. Saving throw modifier: 0. This is not an unusual magical effect.
* An illusion of a pile of sticks that bursts into green flames; the flames then change into a miniature replica of a purple castle with frog's legs; the castle tap dances, and finally turns into a pumpkin with the subject's face before disappearing in a puff of pink smoke, and the sticks are unburned. Saving throw modifier: +2. This is downright bizarre, easily justifying the higher modifier.
===Flaws===
Illusions are seldom perfect, and wary subjects will always be alerted to an image's illusionary nature by its imperfections. For instance, if a wizard uses a spell such as phantasmal force to create an illusionary creature, the creature might lack one or more obvious sensory elements, such as sound, aroma, or body temperature, which can be a dead giveaway that the creature is only an illusion. In extreme cases, the subject's saving throw can be modified by as much as +4. If the wizard is using a better spell, such as improved phantasmal force, any sensory elements lacking in the illusion will not be as obvious, and the subject's saving throw rarely will be modified by more than +2.
Examples:
* An illusion of a bee. Saving throw modifier: +1 (phantasmal force), 0 (improved phantasmal force) . The illusionary bee won't buzz in a lower-level illusion, but it will in the higher-level spell.
* An illusion of a hissing fire lizard covered with filth. Saving throw modifier: +4 (phantasmal force), +1 (improved phantasmal force). The lower-level illusion won't be able to duplicate the lizard's hiss, body heat, or the smell of the filth. The higher-level spell will do a better job, but the modifier assumes that at least one of these elements is imperfect or missing.
==Revealed Illusions==
As explained on page 84 of the Player's Handbook, if one subject successfully disbelieves an illusion and informs another subject of the illusion, the second subject receives a modifier to his saving throw. The amount of this modifier depends on the reliability of the informant and the magnitude of the illusion. If the informant in unreliable and the illusion is formidable (for instance, an illusion of a deadly monster), the subject might ignore the informant entirely; in this case, no special saving throw modifier applies. If the informant is reliable (the subject's commander or friend), and the illusion is relatively minor (such as the image of a small fire), the subject's saving throw can be modified by as much as +4
==Intelligence==
It makes sense that a highly intelligent wizard would be able to create more effective illusions. It also makes sense that subjects with low intelligence would be less likely to disbelieve an illusion. Therefore, if the caster's Intelligence is exceptionally high (18 or more), the subject's saving throw might be modified by -1. If the subject's Intelligence is exceptionally low (7 or less), his saving throw might be modified by -1. A -2 modifier is possible if both the caster's Intelligence is high and the subject's Intelligence is low.
Remember also that characters with exceptionally high Intelligence are automatically immune to low-level illusions. These immunities are summarized on Table 4 of the Player's Handbook.
==The Illusion-Casting Subject==
Characters and creatures who can cast illusions themselves are much harder to fool.  If the subject is an illusionist NPC or a creature with illusion-casting abilities, he receives a +1 bonus to his saving throw
==Summary of Modifiers==
For quick reference, Table 14 summarizes all of the situations described above, giving a range of possible modifiers to the subject's saving throw. Again, these are sugggestions only, not hard and fast rules, and the DM is free to tinker with them as he sees fit. These modifiers are not necessarily cumulative; in fact, modifying any saving throw for disbelieving illusions by +4 is unusual, while modifying a throw by +6 (or more) should occur only in the most exceptional circumstances
 Table 14: Summary of Possible Modifiers for Saving Throws vs. Illusions
Factors ofIllusion 	ModifierRange forSubject
Complexity (use oneof the following): 	
Non-living 	0 to +2
Living 	0 to +3
Magical effects 	0 to +2
 	
Flaws (use one of thefollowing): 	
phantasmal forceor similar spell 	0 to +2
improved phantasmalforce or similar spell	0 to +4
 	
Intelligence of casterand subject 	-2 to 0
 	
Illusion-casting subject 	+1 to 0