Below, I present my theory of how the school of Illusion works. I do not offer any justification, simply state the facts. In particular, I don't indicate where this theory differs from the official TSR policy. If you want justification, read the TSR discussion
Since TSR has divided the school of illusions into illusions and phantasms, it makes it difficult to distinguish between the two different meanings of illusion (school or magic type). To avoid confusion, I will always make it explicit, by referring to the school of illusion, or illusion magic, depending on whether I am refering to all types of magic within the school of illusion, or the specific type of magic affecting sensory perception.
The school of Illusion consists of three sub-schools:
The various spells in the school of Illusion can be divided into five different categories, as follows:
Spells in this group use illusion magic to modify sensory perceptions, and phantasm magic to make these perceptions more believable. The content of the illusion is dictated by the caster, either via real-time mental control, or via a visualized sequence of events. Although concentration is not strictly necessary for all of these spells, the most flexibility and realism is obtained when the caster is actively concentrating on the content of the illusion.
Due to the flexibility allowed by these spells, they can be extremely powerful, depending on the creativity, intelligence and (general/specific) experience of the caster, as well as the recipients.
All of these spells affect all creatures within a certain area of effect. This means that the spell is not targeted at specific individuals, so the caster does not need to know of the existence of an individual for the illusion to affect that individual. However, the caster must maintain a 3-D image of the desired illusion at all times. Normally, such a task would be impossible for even the most profoundly intelligent of individuals, because people are very much used to seeing others from one perspective, not all possible perspectives. However, the spells in this category provide more than just the ability to affect the sensory perceptions of individuals; they also substantially increase the spatial-temporal capabilities of the caster, allowing calculations of 3-D images that would normally be impossible.
Determining whether targeted individuals detect and disbelieve these types of spells can be a difficult process. Rules for handling this are discussed later. However, note that since these spells only affect individuals within the area of effect
This category of illusion spell is usually the reason why individuals decide to specialize as illusionists. Illusionists are by nature creative and imaginative, and have excellent spatial-temporal abilities to begin with. The augmentations provided by these spells tend to be extremely appealing to such individuals, and the challenges in maintaining a complicated illusion becomes its own reward.
This group represents spells that are specialized versions of the concentration category above. As such, spells in this group use illusion magic to modify sensory perceptions, and phantasm magic to make these perceptions more believable. The amount of control the caster has over the illusion content is severely limited, but the power of the resulting illusion is much greater than a similar concentration-based spell.
Spells in this group use phantasm magic to modify the feelings, emotions and/or beliefs of targeted individuals. Illusion magic may be used to augment these feelings, emotions or beliefs via sensory perception modification, but the primary effect of the spells in this category are due to phantasm magic.
Spells in this group use illusion magic to conceal objects or entities from sensory detection and other forms of detection. Depending on the specific spell, phantasm magic may be (strongly) used to emphasize belief in one sense over another (for example, vision over touch).
Spells in this group draw energy from the Plane of Shadow, creating an actual physical force that causes real damage, and that exists independent of the belief of target individuals. Almost all of the spells in this category use illusion and phantasm to make the spell even more potent, but even individuals not affected by the illusion and phantasm components will still be affected by the shadow magic.
Here is a table listing all of the illusion spells from PHB2, and their categories in my theory.
Concentration | Sensory | Phantasm | Concealment | Creation |
---|---|---|---|---|
Phantasmal Force | Change Self | Nystul's Magical Aura | Invisibility | Minor Creation |
Improved Phantasmal Force | Blur | Spook | Invisibility, 10' Radius | Shadow Monsters |
Spectral Force | Audible Glamer | Leomund's Trap | Improved Invisibility | Demi-Shadow Monsters |
Advanced Illusion | Ventriloquism | Misdirection | Vacancy | Major Creation |
Permanent Illusion | Fool's Gold | Whispering Wind | Shadow Door | Shadow Magic |
Programmed Illusion | Mirror Image | Illusionary Script | Mirage Arcana | Demi-Shadow Magic |
Wraithform | Fear | Veil | Shades | |
Illusionary Wall | Phantasmal Killer | Mass Invisibility | Shadow Walk | |
Seeming | Hypnotic Pattern | Sequester | Simulcrum | |
Project Image | Rainbow Pattern | Screen | ||
Dream | Hallucinary Terrain | |||
Eyebite | ||||
Mislead | ||||
Weird |
Both illusion magic and phantasm magic work solely on the minds of targeted individuals. As such, they only work if the targets believe that the induced sensory perception, emotion, feeling or belief is real. In terms of game mechanics, disbelief is determined by a saving throw versus spells, with various modifiers applied based on the caster, target, and situation. Detection is determined either by DM decision, or by an ability check (usually against intelligence, to represent observation skills).
Normally, individuals believe their own senses, emotions, feelings and beliefs, because these are internal properties that are considered inviolate. Thus, chances to disbelieve an illusion or phantasm are not automatic; the targeted individual must detect some anomaly that justifies disbelief. This can be inconsistencies between different senses, unexplained feelings, and concious monitoring of ones internal state. In terms of game mechanics, detection is usually determined by intelligence checks.
If detection occurs, the exact effects depend on the category of spell, and, in some cases, the specific spell, in question. In most cases, detection allows a chance for disbelief (i.e. a saving throw), and if the save fails, the character ignores the anomaly or whatever inconsistency was detected. However, if the save succeeds, the individual knows the illusion/phantasm for what it is. In such cases, the individual can still experience the effects of the illusion/phantasm, but can also decide not to experience them. The illusion/phantasm loses all potential to cause distraction or any other effect on the individual, even when the individual is experiencing the illusion, unless they intentionally fully submerge themselves in the illusion again with a concious act of will.
For concealment spells, the chance that individuals will remember detected anomalies if they fail their chance to disbelieve is dependent on how much phantasm exists in the magic. Low level concealment spells have very little phantasm, so, for example, detecting an invisible individual but failing to disbelieve does not mean that the target forgets about the anomaly - they will know that someone is around, but invisible. On the other hand, if they also manage to disbelieve the illusion of invisiblity, they will actually be able to see the supposedly invisible individual.
All of the above discussion applies only to illusion and phantasm magic. Shadow magic is real, and disbelief has no effect on its reality. However, most spells use shadow magic in conjunction with illusion and or phantasm magic; disbelief of the illusion/phantasm component will imply that no damage from that component is sustained.
Obviously, a well rendered illusion of a monster is believable, but if only illusion magic is used, there is no way to generate the illusion of a 10th level fighter, rather than just an illusion of a person wearing armor and carrying weapons. However, phantasm magic modifies emotions, feelings and beliefs, so, in conjunction with the sensory illusion of a person wearing armor and carrying weapons, phantasm magic can make targets believe that the illusion has a high (or low) degree of skill.
It is possible to make an illusion of a particular monster, or a character of a specific class and level, whenever a phantasm component exists in the spell. The phantasm magic is used to convince the target(s) that the image seen is skilled. In general, how skilled the target believes the illusion to be depends on both the targets past experiences with real versions of the illusion, and the skill-level of the caster.
It is usually more difficult to create an illusion of reality than an illusion created entirely from the mind of the caster. For example, creating an illusion of a specific person is more difficult than creating an illusion of a generic person.