Major image of a dense cloud

[Spiritchaser]

Imagine if you will that a player creates an illusion of a small dense fog/dust/smoke cloud, thick enough to grant full obscurement.

Imagine also that this cloud is placed to envelope a number of foes.

Major image states that physical interactions with the illusion reveal it to be an illusion because objects pass through it, but in the case of smoke or fog, this logic breaks down. It is logical for things to pass through smoke or fog.

There are some potential play balance implications of this, though I’m not sure there’s a problem for a 3rd level spell

[mucat]

Imagine if you will that a player creates an illusion of a small dense fog/dust/smoke cloud, thick enough to grant full obscurement.

Imagine also that this cloud is placed to envelope a number of foes.

Major image states that physical interactions with the illusion reveal it to be an illusion because objects pass through it, but in the case of smoke or fog, this logic breaks down. It is logical for things to pass through smoke or fog.

There are some potential play balance implications of this, though I’m not sure there’s a problem for a 3rd level spell

I'd probably split the difference, and give people in the fog a passive investigation check to notice discrepancies in the illusion, rather than either auto-noticing or making them spend an action on an active investigation check. As you say, the fact that you can pass through fog does not in itself beggar belief, but on the other hand, any flaws in the illusion are quite literally right in your face.

[Segev]

I'd probably split the difference, and give people in the fog a passive investigation check to notice discrepancies in the illusion, rather than either auto-noticing or making them spend an action on an active investigation check. As you say, the fact that you can pass through fog does not in itself beggar belief, but on the other hand, any flaws in the illusion are quite literally right in your face.

This is one of two ways I'd run it, with the other being that any action they take that is hindered by the cloud gets a (possibly secret, if I need to conceal from a player that he's interacting with an illusion) Intelligence(Investigation) check as part of the action. This is just how I would probably do it, not a recommendation that it be everyone's method, but I would likely even use the d20 roll the player made for whatever action he was doing, and then (ideally by knowing these numbers without asking him) apply his Intelligence modifier and, if proficient in Investigation, his proficiency modifier to the raw d20 roll, secretly making his action "really" be the Investigation check while letting it be his roll doing it. (if he happens to also succeed at whatever else he was trying to do, I'd let him keep that success, too; the way he succeeded just happened to also reveal the illusion for what it is.)

[JonBeowulf]

The Silent Image debate has finally grown up. Thank you!

I'd have no problem allowing a 3rd level spell to create the illusion of a cloud. The 20' cube thing might be an issue, but it's one the player has to figure out... or the DM, if they want to use this tactic.

I like the passive INT(Investigation) check suggested above. I'd probably grant an active check if they are attacked while inside the illusion.

[Chronos]

I interpret the "physical interaction reveals the illusion" to mean an interaction of a sort that wouldn't be possible with the real thing, so for an illusion of a cloud, arrows going through it or even walking into it won't automatically reveal it. There will still be flaws, like the cloud not swirling properly around things passing through it, but to notice those flaws, you have to spend your action to investigate it: As in, your action is investigation; it doesn't just get tacked on to some other action for free. You wouldn't necessarily have to say "I'm using the Investigate action", of course: It could also be things like "I take a good look to see if I can find a source for the fog", or "Does this look like the result of a Fog Cloud spell?", or "ooh, fun! I'll play with the fog for a while".

For a Silent Image of a cloud, walking into it would reveal it, for all but very unintelligent or inexperienced creatures, because you'd notice the lack of dampness. But Major Image has that covered, since it includes thermal effects.

[Sigreid]

Here's the thing, foes in the cloud wouldn't feel the moisture a cloud that thick would have.

[Spiritchaser]

I interpret the "physical interaction reveals the illusion" to mean an interaction of a sort that wouldn't be possible with the real thing, so for an illusion of a cloud, arrows going through it or even walking into it won't automatically reveal it. There will still be flaws, like the cloud not swirling properly around things passing through it, but to notice those flaws, you have to spend your action to investigate it: As in, your action is investigation; it doesn't just get tacked on to some other action for free. You wouldn't necessarily have to say "I'm using the Investigate action", of course: It could also be things like "I take a good look to see if I can find a source for the fog", or "Does this look like the result of a Fog Cloud spell?", or "ooh, fun! I'll play with the fog for a while".

For a Silent Image of a cloud, walking into it would reveal it, for all but very unintelligent or inexperienced creatures, because you'd notice the lack of dampness. But Major Image has that covered, since it includes thermal effects.

I think that from a strict application of logic, this feels the most correct, however it does open up a play balance issue.

Given that this is a 3rd level spell it might be ok, but it could be quite strong.

If the casters party has had this tactic explicitly clarified for them it is quite reasonable to imagine that most encounters will occur in scenarios where most opponents are effectively unable to see the players, and where the players can see their opponents.

I don’t want to get too far into the tactics of positioning the cloud (in most cases it probably makes more sense to put it around the players not the foes, it won’t always catch everyone etc. etc.) but at its heart it effectively provides a strong combat buff, quite possibly across 2+ encounters, and it isn’t something most intelligent monsters would “expect” to be an illusion, so even a group of drow might get pounded for a while before they tried to dispel or disbelieve.

As such, having some kind of save (as suggested by others) if a foe were inside the fog, might be wise from a balance point of view.

On the other hand, it IS a third level spell, it is slow to move, takes concentration etc.

[DevilMcam]

Fog cloud is a lvl1 spell so I don't see any balance issue with that

[Amnestic]

If smoke is thick enough that you can't see anything at all - not even an inch in front of your face - it's thick enough that you would feel the difference vs. air when you step into it/it envelops you. And if you could see an inch in front of your face, you'd see that the illusion didn't respond to your movement.

That's a physical interaction.

[Segev]

If smoke is thick enough that you can't see anything at all - not even an inch in front of your face - it's thick enough that you would feel the difference vs. air when you step into it/it envelops you. And if you could see an inch in front of your face, you'd see that the illusion didn't respond to your movement.

That's a physical interaction.

1) Arguably, the temperature effects would be sufficient to give the "feel" of the fog.
2) No, you wouldn't see fog react or fail to react to your movement if you're inside it, even if you can see a few feet in front of your face. It isn't a swirling mass before your eyes; it's a uniform gray fuzz.

[elyktsorb]

Major image states that physical interactions with the illusion reveal it to be an illusion because objects pass through it, but in the case of smoke or fog, this logic breaks down. It is logical for things to pass through smoke or fog.

There are some potential play balance implications of this, though I’m not sure there’s a problem for a 3rd level spell

There is 1 problem with that line of thought, fog and smoke don't move 'through' people, it moves around them. An illusion of fog would move through someone.

Not to mention fog often moves very distinctly around people when they move, and according to the spell you need to spend an action to finely articulate the image, but how would you do that when you can't see the people in it?

They are going to breath in, and the fog isn't going to go in their mouths.

They aren't going to feel the wetness of the fog on them, because they can't feel it since it's not real.

Sure, I'm certain plenty of creatures aren't going to bat an eye at it, but there are reasons they would be able to tell it's not actually fog.

Smoke would be very easy to be like 'wait, I'm surrounded by smoke but my eyes aren't burning and I'm not coughing'

Fog is more likely to confuse.

[Amnestic]

1) Arguably, the temperature effects would be sufficient to give the "feel" of the fog.

There's a difference between humidity (fog is water droplets in the air, after all) and temperature so, no. Spells only do what they say.

[Spiritchaser]

Fog cloud is a lvl1 spell so I don't see any balance issue with that

The balance issue is that this fog is one sided. The casters party knows that this is an illusion so for them, the fog is translucent

In many encounters, It’s almost analogous to darkness + devil’s sight for the whole party. (Albeit with significantly more movement limitations)

That’s potentially quite strong, even for a third level spell

[Spiritchaser]

There's a difference between humidity (fog is water droplets in the air, after all) and temperature so, no. Spells only do what they say.

Ice fog inside a cloud at the top of a temperature inversion would cover this off nicely, plus it’s quite attractive. We can create a very strong smell of smoke or dust (just not enough to cause status effects)

Major image has a lot of options. I think the description of the spell dictates enough illusory power that we can probably fool most creatures with some variation of fog or smoke, it’s more an issue of “should we”, or at least, should we, for play balance reasons, allow some additional save option.

[elyktsorb]

Major image has a lot of options. I think the description of the spell dictates enough illusory power that we can probably fool most creatures with some variation of fog or smoke, it’s more an issue of “should we”, or at least, should we, for play balance reasons, allow some additional save option.

Game wise it's very simple

"Physical interaction with the image reveals it to be an illusion"

Regardless of what the image is, as soon as someone touches the illusion, it is revealed to be an illusion. If your already touching the 'fog' as soon as you move at all it should be revealed, as you will go through the illusion. Spell wise, this is reacting to being touched at all, and has nothing to do with the person realizing the illusion is fake or not. As the point of an illusion is usually to distract or convince someone of something.

If I make an illusion of a door, and someone attempts to grab the knob, the illusion reveals it's self.

In this case, it's someone trying to circumvent the function of the spell by saying that as long as the targets don't think it's an illusion when they touch it, they can't tell the difference, but that's not how the spell works, they touch the illusion, it is revealed to be an illusion.

I could make an illusion of air, completely invisible, as soon as someone touches it, it becomes translucent to them.

Ultimately you could just make a 'fog' in front of the enemies, that way they can't see through it, they aren't touching it, and you all know it's an illusion and can shoot through it with no issue. Sure, that's circumvented by them going around or through it, but so is a regular fog cloud.

[Spiritchaser]

Game wise it's very simple

"Physical interaction with the image reveals it to be an illusion"

Well no.

You are removing a portion of the rule, and the portion of the rule you have removed changes the meaning of the rule.

The rule does not state: “Physical interaction with the image reveals it to be an illusion”

The rule actually states “Physical interaction with the image reveals it to be an illusion, because things can pass through it”

There is no logical conflict with passing through a fog cloud

Now, we can say that we should ignore the second part of the rule for (possibly good) reasons, but the second part of the rule exists and needs to be considered.

I’m not saying that your in game interpretation of what should happen is a bad ruling, only that it is in no way black and white.

[Amnestic]

Ice fog inside a cloud at the top of a temperature inversion would cover this off nicely, plus it’s quite attractive. We can create a very strong smell of smoke or dust (just not enough to cause status effects)

Neither of those adequately deal with the touching situation. It being cold doesn't change the feel. Cold dry air feels different to cold wet air.

[Spiritchaser]

Neither of those adequately deal with the touching situation. It being cold doesn't change the feel. Cold dry air feels different to cold wet air.

Ice fog mostly just feels cold, smoke doesn’t feel much like anything, and we can add smoke or dust smells

[MagicMask]

Well no.

You are removing a portion of the rule, and the portion of the rule you have removed changes the meaning of the rule.

The rule does not state: “Physical interaction with the image reveals it to be an illusion”

The rule actually states “Physical interaction with the image reveals it to be an illusion, because things can pass through it”

There is no logical conflict with passing through a fog cloud

Now, we can say that we should ignore the second part of the rule for (possibly good) reasons, but the second part of the rule exists and needs to be considered.

I’m not saying that your in game interpretation of what should happen is a bad ruling, only that it is in no way black and white.

Moving around in a cloud of fog and passing through a cloud of fog are not exactly the same thing. A cloud is still solid particles of condensed water vapor. The particles are spaced out enough and will move around you such that you can easily move around in the cloud. I think interacting physically with an illusory cloud would reveal it as an illusion.
The best use of this in combat would likely be to shroud your party in an illusion. The illusion impairs the enemies vision at range while the party can attack un-obstructed because for anyone in the cloud it is instantly revealed as an illusion.

[elyktsorb]

The rule actually states “Physical interaction with the image reveals it to be an illusion, because things can pass through it”

There is no logical conflict with passing through a fog cloud

There is logical conflict because fog does not go through people, which is what an illusion of fog would do if you tried to touch it.

By that argument, if you surrounded them with water, they wouldn't be able to tell because you can move through water. Or fire for that matter, or flour, light, even air, which they wouldn't be able to see anyway.

Not to mention, it's not 'logical' conflict, if you touch the illusion, it is revealed to you because you pass through it. Even if the illusion were air, and they couldn't see it, they'd still be passing through it. No matter what you create as an illusion, everything can pass through it.

You can't actually go through anything unless it's ethereal in some way, because you don't actually go through real fog, you displace it.

[Demonslayer666]

Imagine if you will that a player creates an illusion of a small dense fog/dust/smoke cloud, thick enough to grant full obscurement.

Imagine also that this cloud is placed to envelope a number of foes.

Major image states that physical interactions with the illusion reveal it to be an illusion because objects pass through it, but in the case of smoke or fog, this logic breaks down. It is logical for things to pass through smoke or fog.

There are some potential play balance implications of this, though I’m not sure there’s a problem for a 3rd level spell

As a DM, I would not have any issues with this fooling the unintelligent foes. I might give an intelligent one, or a very preceptive one a chance to notice something is off with the cloud, and then, depending on the situation, they may try to investigate it further to see through the illusion.

It also wouldn't last long if they figure out the party isn't hindered by it.

[Spiritchaser]

There is logical conflict because fog does not go through people, which is what an illusion of fog would do if you tried to touch it.

By that argument, if you surrounded them with water, they wouldn't be able to tell because you can move through water. Or fire for that matter, or flour, light, even air, which they wouldn't be able to see anyway.

Not to mention, it's not 'logical' conflict, if you touch the illusion, it is revealed to you because you pass through it. Even if the illusion were air, and they couldn't see it, they'd still be passing through it. No matter what you create as an illusion, everything can pass through it.

You can't actually go through anything unless it's ethereal in some way, because you don't actually go through real fog, you displace it.

We’re departing from rules to rulings here, which is fine, though we need to be aware that’s what we’re doing.

If (and this is not in any way a given) you can see the individual particles? There could be a chance to observe motes moving around your hand or not, but that would be far more in line with “chance to observe and disbelieve” there’s no requirement for the illusionist to arrange things as such.

The distinction you are making between moving your hand through fog, as used in ordinary language, and moving your hand “through” the fog as would happen here is noted, but again that is begging a departure from ordinary language, and requires some assumptions about what the fog/dust/smoke would look like and what would be noticed.

It isn’t the black and white you are suggesting. I’m not convinced it’s even a particularly dark shade of grey.

Now again, there may be good play balance reasons why we might want to read logic like this into the spell.

[Tanarii]

Physical interaction is physical interaction. They become aware it's an illusion.

DM needs to rule on if it's the people who make the physical interaction, only those that perceive the interaction, or if it's everyone for any physical interaction of any kind.

DM also needs to rule if physical interaction makes it go faint as per an Intelligence (Investigation) check, or if they just become aware it's an illusion.

Putting those two rulings together, you probably end up with a common combination and a less common one:
A) Physical interaction makes it go faint, but only for those interacting (or perceiving the interaction).
B) Physical interaction only identifies an illusion. It still takes an Int (Investigation) check to make it go faint.

In this case, ruling combination B makes the illusion still very useful as concealment, since folks need to use it against enemies. For ruling A, it's better to put it over yourself, so you can see out but the enemy can't see in.

[Spiritchaser]

Physical interaction is physical interaction. They become aware it's an illusion.

This is only part of the rule, the full text does state that physical interactions will reveal the illusion because things can pass through it

I’m going to assume that those last few words are important. In the normal case a foe interacts with an illusion and passes through something that should not be passed through. As such they reveal that the illusion is just that.

That’s not the case here.

The text of the rule its self clearly defines a stated condition as justification (again, that’s directly in the rule) That condition does not occur here. That maybe isn’t 100% definitive in determining that a rule does not apply but it’s pretty darned strong.

[Amnestic]

Are you interacting with fog or smoke when you're inside it? Yes. It passes through you, after all.

Ice fog is still water crystals suspended in the air that freeze on contact with a surface (which it wouldn't do, since it's an illusion). Smoke wouldn't interrupt normal breathing and itself couldn't be blown or swirled.

RAW is clear: You pass through the physical phenomenon, therefore you disbelieve it. That still applies whether it's fog or smoke or air or light.
RAI, in the case of fog and smoke is also clear: the physical effects of it you would see if it were real don't occur, so therefore you disbelieve it.

(also in the case of light it's also clear: since it passes through you and is pervasive the moment you blinked you'd notice that the light was passing through your eyelids, thereby disbelieving it)

[JackPhoenix]

As someone who was cleaning the insides of his computer yesterday, I can tell you you can feel the dust in the air long before the cloud becomes opaque.

[Willowhelm]

This is only part of the rule, the full text does state that physical interactions will reveal the illusion because things can pass through it

I’m going to assume that those last few words are important. In the normal case a foe interacts with an illusion and passes through something that should not be passed through. As such they reveal that the illusion is just that.

That’s not the case here.

The text of the rule its self clearly defines a stated condition as justification (again, that’s directly in the rule) That condition does not occur here. That maybe isn’t 100% definitive in determining that a rule does not apply but it’s pretty darned strong.

That condition does occur here.

If you fire an arrow into a “real” cloud like this, it will swirl and deflect the fog or smoke around the arrow as it passes into the cloud. The particles that make up the cloud move out of the way, the air currents buffet them and eddies spread out. It exhibits all the behaviours we’d expect from fluid dynamics.

If you fire an arrow into a major image of a cloud it disappears into it. The illusion doesn’t move or react. The same specks of smoke or fog or mist are hanging in the air in the same place as before. The arrow passes right through them.

Whether the DM rules that this is instantly clear or there is a DC to beat with a passive check etc… that’s up to them.

I can pass through a real bead curtain just fine (but it will move). If the bead curtain passes through me when I try… it’s an illusion. This is the same, just at a different scale.

[Tanarii]

This is only part of the rule, the full text does state that physical interactions will reveal the illusion because things can pass through it

Things don't pass through fog or smoke. They move it aside and otherwise interact with it. Colloquially we may refer to it as that, but it's not what's actually happening.

Like I said, physical interaction is physical interaction. I've seen your argument made enough times now to realize they made a mistake in trying to explain what physical interaction entails with an illusion.

[Segev]

There's a difference between humidity (fog is water droplets in the air, after all) and temperature so, no. Spells only do what they say.

You actually tend to sense humidity through temperature before anything else. I would certainly allow an Intelligence (Investigation) check that successfully pierces the illusion to recognize it due to the lack of humidity, but if you lowered the temperature of tight clothing in a small area of skin, most people would think something had spilled on them, at least until they investigated. Humidity is mostly determined by how well we can regulate heat in relation to the atmosphere. In other words, via temperature.

[chiefwaha]

Correct me if I'm wrong, but isn't it just an image? It doesn't fill the entire area with a cloud of fog, it just fills the perimeter with the picture of it. So enveloping enemies would restrict vision into and out of the perimeter only, not create obscurement throughout the area. At least that's how I always picture it.