How do illusions work?

[Surgo]

Let's say I cast Persistent Image to get an artifact sword that always kills whoever it strikes, and give it the script to follow my hand around, and then I strike somebody and they fail their "save for disbelief" spell. What happens then?

I'm really just having a hard time figuring out how illusions are supposed to work in general The whole "n% real" thing doesn't make a whole lot of sense either.

[Kaelik]

N% real thing is not very good, but as for your situation:

Suddenly they realize that your totally awesome sword doesn't actually cut people, because they see it pass right through them. So either they decide it's probably not real, or it's the Tensaiga. And they keep kicking you in the face.

I wonder what you think "an artifact sword that always kills whomever it strikes" looks like, and why it would be so distinctively and obviously that and not something else, so that even people with no ranks in knowledge arcana or spellcraft who have never heard of such a sword would just see it and know that it must be that.

[TOZ]

They don't. It's entirely at the mercy of the referee.

[CatharzGodfoot]

Let's say I cast Persistent Image to get an artifact sword that always kills whoever it strikes, and give it the script to follow my hand around, and then I strike somebody and they fail their "save for disbelief" spell. What happens then?

I'm really just having a hard time figuring out how illusions are supposed to work in general The whole "n% real" thing doesn't make a whole lot of sense either.

First, your target might not know of this instagib artifact. It's just a magical looking sword. Second, there are plenty of effects like the merciful enhancement, damage reduction, and bladeweave which will cause a direct sword strike to leave no wound. Hell, there are even swords that heal on a strike. The target will most likely assume that it's some strange magical effect (which would be correct).

[TavishArtair]

The persistent image spell does not say it can convince anyone of informed abilities, it only gives you the ability to describe it, and it is up to them to convince themselves of any of the following beliefs (most people will rapidly convince themselves that a flaming sword will burn them)... So I would rule that it would fail to work due to false principles.

[Surgo]

Okay, let's assume there's an artifact that everybody knows about that does kill whatever it touches. And that it's distinctive and what not. Hypothetical situation and all that.

[Rathe]

So...you cast a persistent image of the Sphere of Anhillation?[/i]

[hogarth]

Okay, let's assume there's an artifact that everybody knows about that does kill whatever it touches. And that it's distinctive and what not. Hypothetical situation and all that.

Then you have a figment of that object with visual, auditory, olfactory, and thermal components. Note that "touch" and/or "pain" and/or "annihilation" is not in the list.

The only iffy one in that list is "thermal"; can you create an image of the inside of the sun, complete with thermal effects? I'd probably file that under Phantasmal Killer, I guess.

[CatharzGodfoot]

Okay, let's assume there's an artifact that everybody knows about that does kill whatever it touches. And that it's distinctive and what not. Hypothetical situation and all that.

I'll answer your hypothetical situation with another hypothetical situation:
Let's assume there's an artifact that everybody knows about that does kill whatever it touches. And that it's distinctive and what not. And then someone makes a perfect look-alike stage replica of it, and whacks somebody with it. What happens?

[K]

In the Red Box, illusions used to work the way Surgo wants them to. You could cast an illusion of a petrifying attack from a Gorgon or something, and people with gorgon experience would freeze in place thinking they were paralyzed. It even made monsters with AC and HPs.

In 3.X, illusions cover exactly what they say they cover. Disbelief means that suddenly some switch in your head flips and rather than seeing an illusion, you get to see a wispy outline of whatever they wanted you to see. I imagine it is like seeing one of those "magic eye" pictures that look like nonsense until you unfocus your eyes and suddenly see a boat or a ducky or something.

But when you believe an illusion, you see and experience what those illusions say you do. Sometimes, this includes contradictory information.

For example, you see an orc running at you. As he gets closer, you notice he is not making noise as he runs.

Now, maybe he's an illusion. Maybe he's under a Silence spell. Maybe he's incorporeal. Frankly, you don't know, and you don't even get a save until you can put hands on it or shoot arrows or cast a spell on it, or otherwise interact with it (and no, sight doesn't count.... but there is a PrC that lets you get a save when seeing an illusion).

Touch and thermal illusions are probably the hardest to understand. I mean, how can you touch something that has no substance? Or feel the heat of something that doesn't burn?

The trick is to understand that when you touch a touchable illusion, it has no substance but you act like it does. A person will act like they feel the weight of an illusionary object they are holding in the same way a mime might. They might even lean on an illusionary wall without ever putting their weight on it (though pushing something through it would work).

Thermal illusions make you feel hot or cold, but can't hurt. So you believe an illusionary wall of fire is a wall of fire, and might even believe that after you stick your hand in it and don't feel any pain. I mean, maybe someone cast a Resist Energy spells on you, or that spell is keyed to not hurt members of your race. Frankly, you don't know and "illusion" is only one choice on the list.

Now, within those limits illusion still has a huge amount of power. People don't get saves until they interact with something, and then only one save unless someone tries to convince them it is an illusion. This means they might race their horses across an illusionary bridge to their deaths only because they had no reason to even question that the bridge was not real. Illusions of people can be nearly perfect considering that you rarely have a reason to touch other people, so finding out that the sight and sound illusion of the king is not real might be very hard indeed.

So in short, illusions only create the sensations they say they do. How people interact with that information is where the real power resides.

[Surgo]

Thanks, K -- that cleared it up marvelously. (Though I think you're being unfair, as what I said is certainly not how I wanted them to work.)

[Crissa]

I think it's somewhat disturbing that there interaction doesn't include any sense of perceiving.

-Crissa

[CatharzGodfoot]

Thermal illusions make you feel hot or cold, but can't hurtharm. So you believe an illusionary wall of fire is a wall of fire, and might even believe that after you stick your hand in it and don't feel any painget burned. I mean, maybe someone cast a Resist Energy spells on you, or that spell is keyed to not hurt members of your race. Frankly, you don't know and "illusion" is only one choice on the list.

Fixed that for you.

[RandomCasualty2]

Straight up figment Illusions can never hurt you in 3E. Ever.

You need shadow magic for that.

Good illusions generally create something the opponent doesn't want to touch (like green slime), things they probably won't bother to touch (illusionary walls to block a branching corridor) and vision control.

Vision control is effectively a nice way to play with the illusion rules. It involves creating some kind of vision blocker in front of your party, typically a wall or curtain. Your party puts their hand through it for automatic disbelief (meaning they can now see through it). Your enemies on the other hand can't see through it until they actively disbelieve it, which generally requires them to touch it and you can fire through it freely while having full concealment.

Now, depending on the DM, he may or may not count firing an arrow at the wall to be interacting with it, so your opponents may get a save to basically end the effect on them after they shoot it. But you still get them to waste a shot doing that and possibly more shots. And because disbelief is personal, every enemy has to at least waste one shot in this way.

[A Man In Black]

Touch and thermal illusions are probably the hardest to understand. I mean, how can you touch something that has no substance? Or feel the heat of something that doesn't burn?

I don't have a problem with this. It's basically the Gom Jabbar.

[Surgo]

Keith, do you mind if I copy your explanation onto the wiki? An explanation so clear of something that makes so little sense deserves to be spread.

[TOZ]

Fucking illusions, how do they work?

[koz]

Fucking illusions, how do they work?

Damn, beat me to it.

[TOZ]

Thanks for the image backup Sinister.

[K]

Keith, do you mind if I copy your explanation onto the wiki? An explanation so clear of something that makes so little sense deserves to be spread.

Go for it.

[Previn]

Touch and thermal illusions are probably the hardest to understand. I mean, how can you touch something that has no substance? Or feel the heat of something that doesn't burn?

So illusions force you into the role of ultimate mime.

[fbmf]

Got sucked into a "How does Silent Image Work?" argument with an old friend last night, so...

[Raise Thread]
Where does it explicitly state (PHB, FAQ, Sage Advice, whatever) that...

[*]interacting with an illusion is a Standard Action?

[*]that this Standard Action gives you incontrovertible proof?

Also, can you Will Save to Disbelieve without spending a standard action? If so, where does it say that?

Lastly, can someone point me to a step by step explanation of the "I use Silent Image to trap my enemy in an illusionary box, since I can see through the box I make an image on the outside of the box telling my archer friends where to fire, and hilarity ensues" tactic?
[/Raise Thread]

Game On,
fbmf

[Aharon]

Skip's houserule makes it a move action. That's the most official thing I've found when I recently researched this topic.

[Grek]

Lastly, can someone point me to a step by step explanation of the "I use Silent Image to trap my enemy in an illusionary box, since I can see through the box I make an image on the outside of the box telling my archer friends where to fire, and hilarity ensues" tactic?

Step 1. Explain what you are about do to to the party, so that they know in advance that it's an illusion.
Step 2. Cast your figment of a magic box.
Step 3. Ask your MC if being told about the spell by the caster constitutes "proof that it isn’t real" for the purposes of automatically succeeding on the saving throw to disbelieve.
Step 4a. If your MC says yes, the party automatically disbelieves the illusion, rendering it "a translucent outline" for them.
Step 4b. If your MC says no for whatever reason, everyone in the party makes a will save at a +4 bonus to disbelieve the illusion. Everyone that succeeds gets to see through the box as in 4a.
Step 5. Everyone that can see through the box starts shooting.

[CatharzGodfoot]

A spot check to see something that you've missed is a move action (SRD under Spot). Interacting with an illusion requires more than just seeing it, as indicated by the D&D Joke Book on Spot.

So, it seems reasonable that studying as a move action would let you make a will save to disbelieve.

Being able to make a save to disbelieve is not the same as having proof (which allows for automatic disbelief), although a DC 80 Spot check is as good. Even knowing that something is an illusion (because you buddy says that it is) isn't proof, and only lets you make another save with a bonus.

The most important unanswered questions are 'what qualifies an interacting?' and 'what counts as proof?'.

My guess is that 'interaction' is exactly that: taking an action for which you would expect a reaction. This could be poking a pole at an illusory floor (which should have a normal force), yelling at an illusory warrior (which should hear), or kicking an illusory puppy.

Proof is probably more along the lines of falling through an illusory floor.