Like most other gamers, my first experience with roleplaying was with the AD&D(TM) system (actually, I've noticed that many the newest generation of gamers seem to have begun with one of the robot or Vampire games rather than AD&D(TM), but that's a separate topic). For a long time my experience with illusion was casual. If it seemed to be an illusion, you disbelieved it. Alternatively, you touched it with your bare hand to dispel it; some GMs ruled that this was effective. However, none of them used illusion effectively or dramatically. It was never anything more than a different kind of trap or trick.
The one time I played an illusionist I did manage to come up with some interesting uses for the basic illusion spell, (spell name omitted because TSR(TM) feeds their lawyers red meat). The only one that I can recall offhand was really quite simple: an illusion of darkness. A code word said aloud would let the other party members know that the illusion was being cast, giving them an improved chance to disbelieve. But for foes in the area who failed their saving throws, total darkness enveloped them. Needless to say, a party that can see has a huge advantage over blind enemies!
Eventually the GM became irritated with this tactic; it was simply too effective. Creatures began making their saving throws more and more often. Finally, I asked him why my spell had become totally ineffective. He informed me that the rules said that if the illusion produced was not believable, it had little chance of being believed-- and according to him, sudden inexplicable darkness was something that monsters wouldn't buy.
The solution was simple, of course. I simply altered the spell to produce the appearance of a rising cloud of smoke, getting thicker and thicker until it obscured all sight. The apparent source of the magical smoke varied depending upon the circumstances. However, the GM soon decided that this was ineffective, too; this time, however, he refused to explain why. As time progressed, he increasingly ruled against *any innovative use of the basic illusion spell, until there was no point in even trying to cast it. Soon after, I left his campaign.
That was many years ago. Since then, I have applied a variation of that spell in a RuneQuest campaign: as a sorcerer, I used the MultiSpell skill to cast several illusions of darkness simultaneously onto the heads of a number of enemies at once. The effect was only a -10% chance to their visual abilities, but at the time it was the most effective thing a relatively unskilled sorcerer could do. Under the new proposed RQ4 rules, of course, I'd have been even less effective. An illusionist's life is not an easy one...
A while ago, I had a strange idea for a trap using disbelief that would be, well, totally fatal--or damn close to it. It's pretty silly, too. You Have Been Warned. 8^>}
A party fights its way through a typical dungeon, battling monster after monster in an insatiable quest for money, money, money. Down they go, deeper and deeper, hacking their way through level after level of ravenous fiends. Why is population so dense in this desolate locale? Maybe the schools are good. 8^>}
Down the party goes, down through this mysterious underground skyscraper. Strangely, the deeper they go the more powerful the opposition they meet; fortunately, the more powerful the opposition, the greater the amount of treasure to be gained (the monsters must not have anything to spend it on down there. Hmm...a good boutique or convenience store might do well in the dungeon...).
Finally, at the very bottom, they fight the most powerful and deadly monsters of all. Taking punishing losses, they manage to defeat the ghastly things--only to discover a small unlocked chest in an otherwise empty room. Inside the chest is a simple piece of paper. On the paper are the following words:
Hello. I hope you've enjoyed my dungeon. I wish it could have been a real one, but that would have been far beyond the means of a humble illusionist such as myself. Therefore, (over)
This is the last opportunity for the party to avoid death.
(continued from front) ...I've constructed this dungeon entirely as an illusion--right down to the hole. In other words, you're standing hundreds of feet below the surface of the earth in solid rock.
Sorry!
(signed) Bob the Illusionist
Now it's up to the party's disbelief. Can they maintain their belief in the illusion of a dungeon that's keeping them alive long enough to climb back out? Or will they find it impossible to avoid realizing that they are actually buried alive in solid rock?
A kind GM might allow them to make saving throws of some sort. They could keep going as long as at least one member had failed--the disillusioned could be led by those still able to see the dungeon. Alternatively, the GM might simulate the difficulty of avoiding disbelief by ruling that they can live for as long as they are able to speak without, say, using the letters e, i, or o.
I doubt I'll ever use this illusion--it's too deadly, and I don't run dungeon games. And of course it uses illusion magic of a type that transcends most game mechanics. But it *is* amusing. Particularly since even if the party manages to get out, all the treasure they won is illusionary...though the damage isn't.
Another idea on disbelief and illusion--I can't recall if I've used
this one or not, though I think I did. The idea is *layered*
illusions, setting up multiple illusions overlaying and hiding each
other. Disbelieving one reveals the next, and so forth. It seems a
good way to allow a clever player to use simple spells to far more
effect than normally possible--which is what unimaginative gamemasters
hate, of course. 8^>}