In latter-day D&D where Illusionists are just a variety of magical specialist, everything about them makes sense. You might not care for the way they're written up, but they match all the other specialists. But in older versions, and in Labyrinth Lord, they're the only magical specialists. Why Illusionists? What's so special about them? And how do they fit into a campaign milieu and a setting?
I hadn't put any real thought into Illusionists until someone came along and played one in Wampus Country. My first thought was that maybe the theme should be fairy-related, and the whole Illusionist schtick would be fairy glamour. But the spell list for Illusionists contains far more than just illusions. What about color spray? What about all those shadow-related spells 2e Illusionists used to get? And what about that whole "illusion magic is its own language" crap from back in the day?
This is what I came up with...
ILLUSIONISTS OF WAMPUS COUNTRY
Illusionist, mesmerist, trickster, prism-wizard, rainbow sorceror, shadow-mage...
So-called "illusion magic" of Wampus Country is a subset and specialty of several of the better-known arcane sciences, combining magic which affects the senses with powerful spells focused on shaping and manipulating light and shadow. Very few sorcerors specialize in these arts; some are steered toward illusion by fairy ancestry or some other event which contorts the magic-user's mind to make them see the world in this way.
Illusion is a philosophy, not a magical system. Illusionists can read magic in the same way as 'normal' wizards, there's no need for a separate 'read illusonist magic' spell or any of that. Some spells can be cast by both magic-users and illusionists, but there are other dweomers which can only be utilized by illusionists or by 'vanilla' wizards.
The magic mastered by illusionists generally falls into one or more of several categories, listed below with example spells:
Aesthetic/Sensory magic - those ensorcellments which affect the target's senses directly, either by creating the seemingn of something, or by denying the victim the use of one or more senses. Many of these spells function by manipulating the interplay between light and darkness, and this category serves as both a catch-all and a middle ground between the two subschools of illusion listed below. (Auditory Illusion/Audible Glamer, Blindness, Blur, Confusion, Deafness, Doppelganger, Hallucinatory Terrain, Hypnotism, Invisibility, etc)
Prismatic/Rainbow magic - those spells which harness the power of light, especially any which draw on the legendary presence of the cosmic rainbow and its associated powers. (Color Spray, Dancing Lights, Hypnotic Pattern, Illusory Stamina, Prismatic anything, etc)
Darkness/Shadow magic - that handful of enchantments which manipulate and shape mundane shadow and twilight, or draw power directly from the realms of shadows. (Darkness, Fear, Fog Cloud, Implant Emotion, any of the shadow-related spells, etc)
At higher levels of mastery, illusionists are said to specialize in either rainbow or shadow magic as they build strong connections to those mystical realms and find themselves inextricably embroiled in the ancient enmities between light and darkness and becoming a captain in this war - including learning the important ability to project themselves astrally. Witting or not, even the lowest-level illusionist is a pawn in this extradimensional chess game.
Regarding Conjure Animals: I had completely forgotten this was an Illusionist spell, although it makes sense in a rabbit-from-a-hat way. For Wampus Country, when an Illusionist learns this spell, he or she must decide whether it is the "rainbow" or "shadow" version; the animals conjured will be different.
Procuring new spells: As an illusionist, learning new spells can be a pain. You can learn allowable spells from your magic-user buddies, but for the most part you'll need to learn illusion magic from scrolls and from interactions with fairies and creatures of the rainbow or shadow persuasion. Keep an eye out.
|Ilusionists understand the cosmic truth of the prism, and its link to so-called rainbow sorcery from beyond.|
|You won't be making jokes when a high-level illusionist summons a herd of singing rainbow-unicorns to trample your state-of-the-art castle into so much dust.|