Illusion Magic

Changes and extensions to the OSE spellbook rules
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The following discusses Illusion Magic, why it is both powerful and difficult to rule about, and how it is handled in this game.

Illusionary Effects

  • An Illusionary Effect is any effect that misleads the target's core senses - either the traditional five senses or any other sense that the target may possess that is affected by the spell
  • Some Illusionary Effects are either wholly or partially real in that they create real, physical things (e.g. the Wall of Fog spell) or create things formed partially of illusion magic (to fool the senses) and partially of shadow-stuff or some other substance that lends a concreteness to the illusion and gives it the veil of being a completely real and physical thing (e.g. the Phantom Steed spell)

Complexities of Illusion Magic
Illusion magic adds a great deal of interesting spells and effects to the game and provides Wizard-minded characters with an alternate toolset to solve problems, but it is complicated to actually add to the game in practice. Some of these complexities include that illusion magic is:

  • Open-ended: illusion magic is often ill-defined or intentionally undefined, leaving what is created up to the caster's imagination
  • Caster Knowledge-based: without explicitly saying so (at least in some cases, see the Phantasmal Force spell), illusions are dependent upon what the caster has actually seen, experienced or the like. Questions arise along the lines of: 'Can an Illusionist adequately represent the illusion of a forest fire if they have never personally seen one?'
  • Mind-based: a target's mind is intrinsically tied to its senses. If the senses are fooled, it stands to reason that the mind is also fooled. However, there are many "creatures" (e.g. fungi, insects, golems) that do not have minds per-se. It becomes harder to adjudicate illusions when they affect mindless or even differently-minded creatures. For example, can a golem - a creature literally without a mind or any intrinsic fear of its well-being, be affected by the Spook spell, which makes the caster appear as "a monster from the target's worst nightmares"? Can undead (especially mindless undead like zombies or skeletons) be frightened? Can these creatures be fooled by visual illusions?
  • Target Knowledge-based: What if a caster uses Phantasmal Force to create the illusion of a Medusa? Will this illusion turn targets to stone (or paralyze them as suggested in the spell description) if the target has never seen or heard of a medusa's terrible powers? How does an instinct-driven creature like a giant insect react to a potentially deadly but indirect situation like the visual illusion of a cave in?
  • Sense-specific: some illusions target only once sense (e.g. the Phantasmal Force spell) and others target multiple senses (e.g. the Spectral Force Spell). It is sometimes difficult to determine if fooling one sense is sufficient to actually fool a target. For example, a Phantasmal Force spell can create the illusion of a large fire blocking a doorway in a dungeon. However, there is neither sound nor heat emanating from this fire (whereas the Spectral Force spell does contain these additional provisions). Does this mean that those failing their save against such an illusion can safely ignore it since they know it is not putting off heat despite how realistic it looks to them? In effect, will the targets, even if fooled by the appearance of fire, see it for the illusion that it is since it has no ability to fool the other senses? What if the target is intelligent - let's say a human, with the ability to reason about facts presented to the senses in a much more sophisticated way than let's say a rat might "reason" about what its senses are telling it? As a second example, how does one fool a pit viper - which has a well-known heat sense and sense of smell (through its tongue) and uses these to hunt far more than just its eyes. Does a Phantasmal Force Spell fool all of these senses or just some of them? If ruled that it affects both the 'heat sense' and its eyesight (since both are vision-like), doesn't that intrude on the 3rd level Spectral Force spell, which explicitly adds "heat/thermal" capability to illusions? As a more extreme example, what if an Illusionist created the illusion of a fat piglet wandering into the web of a giant spider. If the spider fails its save and actually perceives the piglet entering its web, but receives no queues that anything is actually entangled in the web because, of course, nothing is, does the spider dash over to the illusionary piglet's location since its web has not indicated a trapped creature is entangled there? Does an illusionary spider inject imaginary poison and if so, should the target be forced to save against this poison?
  • Spell text as written may increase confusion: the spell text itself may be contradictory. For example, the Phantasmal Force spell creates only visual illusions but these illusions, bereft of any other sense component or quasi-real capabilities, can deal damage or otherwise fool the mind sufficiently to incapacitate the target

Adjudicating Illusions
The Referee must adjudicate each casting of each illusion spell and make a ruling about how the spell operates given the totality of the facts. Things to consider in this ruling include:

  • the as-written text of the spell
  • the experience and knowledge of the caster creating the effect
  • the affected senses of the target and how they inter-relate in helping the target understand the world around them
  • the as-written text of other illusion spells that may shed some additional light on the situation at hand (e.g. Phantasmal Force vs Spectral Force)
  • the as-written text and level of non-illusion spells that may have the same or similar effects as the proposed illusionary effects. In general, lower-level illusion spells should not outperform higher level spells that have the same or similar effect
  • the degree to which the illusionary nature of an effect can be communicated among multiple targets (e.g. one target is not fooled by the illusion and informs the others around it)

The Referee should work with the player of the Illusionist to make a ruling that makes the most sense given the totality of facts and is representative of the type of game they want to jointly create. When reaching this agreement, the Referee must keep in mind that illusion magic is actually supposed to be an effective tool in the game and it should offer meaningful solutions to dangers faced by the characters. If the magic is ineffective, no one will use it and there will only be Wizards in the game. Players should keep in mind that illusion magic is tricky to deal with from a Referee standpoint and can lead to slippery-slope rulings in the future and that if illusion magic is in many ways superior to "real" magic, there will be no Wizards in the game and therefore the Referee must place limitations on illusions to prevent them from dominating the game.