Let's say you use an illusion spell to "create a mirror hanging on the wall".
Does this illusory mirror reflect images just as any other mirror naturally would?
Or can it only try to "mimic" what a mirror does if the caster is there to manipulate the image as if it were?
There's all kinds of good illusion conundrums like that. Of course it is up to the DM to decide.
Personally, I think the best way to think of it is that the illusions generally affect the mind of the beholder, not the actual light bouncing off of objects. So an illusion of a mirror could show whatever the caster wanted, but it wouldn't be able to accurately reflect something the caster didn't know about, and any changes in what it showed would need to be manipulated by the caster.
I'm not saying you are right or wrong. In fact, you are absolutely correct that this is squarely in the hands of a DM. Though I consider a great many things to fall in that category.
But the illusions are "mental" thing. Aren't those usually defined as phantasms? I consider normal illusions to be actually conjured, per se, albeit not having substance.
Anyway, thanks for participating in my Thought Provoker!
I'm all for letting active control of an illusion result in the illusion of a mirror reflecting the area the mirror in is, but when it comes to what an illusion of a mirror looks like without active control, I am less certain.
The easiest explanations seem, to me, to be having the illusory mirror look obviously to be a mirror and yet appear to be dirty or damaged in such a way as to not be reflected, or the mirror in question to be a phantasm (and thus in the mind of the victim, rather than on the wall of the room) so that they would see it as they expect to see it and/or rationalize away any discrepencies.
I'd say it depends on the spell used. If it affects only the target and is otherwise nonexistent outside their head, then I'd run it as seeming to be a mirror, but unable to actually reflect things accurately that the caster doesn't know about. This would make any subsequent Investigation checks easier if they recognized this oddity.
If it's a thing cast in space that affects everyone, I'd say it reflects light as normal. As for manipulating light, I'd look at it this way: if there were an illusion of a box, and you stood behind that illusion with a very bright light and shined it at the target's eyes, would their eyes hurt? It's possible to justify, but not how I'd run it. If they can't see through the illusion (or phantasm, or shadow magic construct, or whatever), the light isn't reaching them from the other side. So, that makes a precedent of illusions obstructing light. If the illusion also appears brighter or darker if light is shined on it, that means it's reflecting light. Hence, an illusory mirror can reflect light.
Just how I'd do it, though.
I'd say no. The only illusion spells I can think of that would create the image of a mirror are minor image or major image. Minor image can't create light or any other sensory effect so I would say it cannot reflect light either. Major image can react to it's environment but has to be controlled by the caster.
On the other hand if you cast Fear on a Medusa, it's greatest fear might be a mirror that pursues it wherever it goes. 
jaelis wrote:
My guess is, that you need to keep updating the illusion to give an image of the person. The caster also needs an exact mental image of the person who's reflection is in the mirror and thats extreemly hard (without the keen mind feet). A mole on the wrong cheek or smudge on the forehead is easy to miss.
But never-the-less: Great thought experiment.
CFK wrote:
Here's my concern:
So sure, you say you can create an illusion of a mirror. It does sound reasonable I agree. Presumably with minor image, I guess? It is a small static object so why not?
So great, you come upon a corner in a corridor and you want to know what's around it. Cast an illusion of a mirror! I guess that's OK too, but maybe seems a little powerful for a cantrip with so many other uses.
Uh oh, what's around the corner is a medusa... well we can handle that 
Or to take it another way, if the mirror lets me see around a corner, does that mean an illusion of a torch lets me see in a dark room?
How about an illusion of a window letting me see through a wall?
Or an illusion of a magic portal that lets me see into the king's council chamber?
It's a slippery slope argument, which can be bogus. A given DM can disallow what they don't like and allow what they do like. But you have to put a limit somewhere, and to me it seems simplest to just put it right at the begnning... I say an illusion can't provide any information that the caster doesn't already know.
Despite it being raised earlier the illusion/phantasm divide keeps being misunderstood. An illusion that is not a phantasm really does create a 3d 'hologram' and is NOT just in the victim's mind. See PHB118. Compare Minor Illusion and Fear
lawrencehoy wrote:
I had a similar argument with my DM. I was playing a shadow monk (who can teleport from dim light to dim light)
I was asking him if I can use minor illusion to create a cloud, for example, that would cause dim light on the ground and cause me to be able to teleport there using my shaodw step ability from my shadow monk level 6.
The discussion came to this:
- An illusion require the observor to fail a Intelligent save in order to see the illusion, and creature who cannot see, are not affected by the illusion.
- Physical matter (like your hand, a sword, an arrow) pass trought illusion like if the illusion didn't exist.
So the physical particule of light (photon) can pass trought the illusion without problem (as easyly as the arrow, the sword or the rock can pass trought it)
So if the light pass trought there won't be any dim light created. and observor will see a cloud blocking the sun, but light still reaching trought the cloud and illuminating the room.
The same reasoning can be used for people saying that you can cast a black illusion on a torch so ennemy won't see your light, but since your team see trought the illusion they will be able to see normally. This is also false (for the same reason that the cloud didn't block the sun) the photon still pass trought the illusion and illuminate the room, and the ennemy will see a ball of darkness (hiding the torch) then 20ft radius of bright light and 20 ft radius of dim light.
But your mirror is a little bit harder to rule, since it depend on how does teh illusion affect his targets?
If illusion are a subset of enchantment, modifying the though process center of the brain, then yes the target will see the mirror and will see what he believe his is reflection in it.
But this cannot be true, since illusion are also affecting mindless creature (and usually work even better with them)
So I'm guessing illusion modify the visual perception (and at highier level modify the other sense) of the target in seeing what you want it to see within the size of the illusion. So you create the image of an mirror, but your image is stagnant and require your input (concentration, action, etc... as describe in the spell description) in order to change, so for the mirror to reflect anything the mirror would require the spellcaster input to modify the image, since the illusion itself is unable to reflect the light or to change by itself.
So I would say no you cannot create a workable mirror using minor illusion, for teh same reason that the illusionary grass you create with minor illusion do not dance in the wind and do not react to someone stepping on it
Now for higher level illusion, it would depend on how they work. With the wizard able to make a part of his illusion real, then yes your illusonary mirror that become real for a round will be able to reflect light.
An illusion that you can modify then yes you could manually change the illusion to mimic the reflection of a real mirror (the same way that a programmed image can show
jaelis wrote:
QwertyAzerty wrote:
lawrencehoy wrote:
CFK wrote:
jaelis wrote:
jaelis wrote:
IMO: If you use a static illusion, you could only make a picture of a mirror. You might be able to fool someone looking from a paticular angle, but not anyone walking around.
If you used an animated illusion, you could make a mirror.
mellored wrote:
Hah I still like those torch questions...
If you can't create a mirror that shows reflections, then you can't create a realistic looking... well, anything. Every surface you see is illuminated by a combination of scattered and reflected light, and the ratio of those (and the precise directions etc) give a surface it's texture.
If you want to see the level of illusions possible without reflection, you want to go look at computer games from the era of quake 2. They don't look remotely real.
Similarly with light generation - unless illusions can create light, then illusions of anything that generates light (fire, magic, lanterns, candles etc) will simply not work.
So in my game, an illusionary candle generates light unless the spell explicity states otherwise and lets you see the room around you as it really is. An illusionary mirror lets you see around corners even when you've never looked there before assuming that you want it to.
And the illusory window in a door?
I would say you can't create a visually subtractive illusion without the spell specifically saying you can (such as invisibility). So you can't make a window or a hole in a door. Otherwise you could use the generic illusions to disguise yourself as a person made of air, and skip invisibility entirely...
Of course you can do the wil-e-coyote trick, and pull it off quite well, but it's not likely to fool someone from anything but long range.
ChrisCarlson wrote: