Illusions and Passive Investigation

[Elredion]

The activities the rules call out as obviating a passive Perception check for keeping watch are navigating, tracking, foraging, and map-making. Any similarly distracting activity could do the same. They key thing here is that there is a potential trade-off. You can continually keep watch and gain the benefit of your passive Perception or you can do some other activity and potentially not gain that benefit - choose.

No qualms with that. You can't be engaged with another activity and be attentive and alert with your surroundings.

I read it again and I don't infer that from the feat. Sure, if a monster is taking steps to remain vigilant for the telltale signs of illusions, then the DM could reasonably rule that passive Investigation applies, if the outcome the monster's effort is uncertain. But this level of scrutiny (which probably includes more than just gawking) should come with a trade-off in my view, as above.

This is where I disagree slightly. Just like someone using passive perception shouldn't have to specify that they are looking for traps or stealthed creatures, someone using passive investigation shouldn't have to say "I'm checking for illusions." That to me says more of an active check with dice rolling. Or if you want to take it a step further, a barbarian who really suspects illusion magic taps everything with his maul.

In other words, the fact that it's passive means you're scanning anything and everything for abnormalities. A higher score means you catch more things.

Treating passive Investigation as a form of "always-on radar" strikes me as an attempt to justify making illusions less effective.

Well yeah, that is what it is. It seems to me that a well executed illusion has no counter if you don't use passive investigation. Let me use an example:

An enemy party is holding a noble hostage in his estate. The party consists of two rogues, a wizard, a barbarian, and the leader. The leader, a fighter, says to the party, "Stay here and keep an eye on our hostage. I'm going to check on our sentries posted on the upper levels. Don't do anything until I tell you." The players have a party with an illusionist and gets word from the scout. The illusionist makes a minor illusion of the leaders voice saying "Everybody get up here, there's trouble."

Now there's a few different ways the DM can go about this:

1. The enemy party all rushes to action. The PCs rush to get the hostage out uncontested.

2. The party all makes investigation checks for the source of the sound, checked against the spell DC. The player could argue that the party had "No logical reason" to investigate the sound and they do have somewhat of a point since the leader did just say wait for my next order. Not to mention the enemies would not want to "waste action" investigating when they think they are immediately needed to deal with a threat.

I wouldn't have a problem with the "meta knowledge" solution of NPCs rolling against every player illusion. In fact it seems many DMs do this for stealth and disguises. This does have the effect of slowing the game down however.

3. The enemy wizard is on level with the PC and automatically detects the illusion due to the passive investigation. This creates a new dynamic of having to scout for wizards and high intelligence creatures when attempting illusion trickery. And that perfectly makes sense, those creatures are practiced in magic and should be better at detecting illusions even when they aren't expecting them.

 

[Elredion]

If the DM wants some, all or none of the PCs to see through an illusion that he himself has created, that's fine. That's his job, deciding things like that. He can decide arbitrarily what makes the best narrative to entertain the players. He can reveal the illusion immediately and leave the players to admire it and wonder what it signifies and who the NPC was who supposedly created it; or he can decide to play 'gotcha' and not reveal it unless and until it occurs to a canny player to make an active check. But either way, he doesn't have to justify that decision to himself by appealing to some sort of formula.

If an NPC casts an illusion, the DC is determined by the NPC's stats which the DM decides arbitrarily. There's no element of chance. The PCs skill adjustments are known as soon as they enter play. Again, there is no element of chance. Adding 10 and calling it a passive score doesn't change that. The result of comparing two numbers that are known in advance is a foregone conclusion.

If you use a foregone conclusion to try to justify an arbitrary decision, you are not being honest with yourself. I might decide to wear red socks tomorrow, on a whim. But if I tell you that I had to wear red socks because pi is more than three, you would be entitled to cast doubt on my thought processes.

Passive scores make sense when they are compared to a dice roll (such as a Stealth roll). They don't make sense when they are compared to a predetermined stat (such as a spell save DC) because the comparison is redundant.

That's a very good point, it did cross my mind when brain storming scenarios.

That doesn't cover the illusions created by PCs though and much of the debate is on how powerful those can be when executed cleverly.

Simply put, an illusion crafted so that the NPC has no logical reason to investigate creates a "loophole", where the illusion goes unchecked.

 

[iserith]

This is where I disagree slightly. Just like someone using passive perception shouldn't have to specify that they are looking for traps or stealthed creatures, someone using passive investigation shouldn't have to say "I'm checking for illusions." That to me says more of an active check with dice rolling. Or if you want to take it a step further, a barbarian who really suspects illusion magic taps everything with his maul.

In other words, the fact that it's passive means you're scanning anything and everything for abnormalities. A higher score means you catch more things.

This reveals what I find to be a common misapprehension of what passive checks are for. In my initial post, I quote the rules and what they tell us is that passive checks are for resolving uncertainty as to the outcome of a particular task that is being performed repeatedly. That task must be described by the player like any other action, though sure, it's probably a common and fairly safe assumption at the table that unless the players describe some other action that is sufficiently distracting, the characters are keeping watch for hidden threats (and thus their passive Perception scores might apply to noticing hidden monsters and traps).

Someone who hopes to have his or her character's passive Investigation score apply to resolving uncertainty in a repeated task similarly needs to describe what the character is doing (approach) and hopes to achieve (goal). That is so the DM can decide what, if any, rules apply and narrate the result of the adventurer's action (Basic Rules, page 3). The example of the barbarian is a good one: He is tapping everything with his maul (approach) so as to uncover illusions (goal). Here we have a character performing a task repeatedly and although outright success seems like it might be an appropriate ruling, a DM who finds the outcome is uncertain can now use the character's passive Investigation score to determine an outcome.

So the questions I think the DM should ask himself or herself when adjudicating the player's stated action for the character is: (1) Is this effort successful, unsuccessful, or uncertain? and (2) If uncertain, is the character performing a task repeatedly? If the answer to (2) is Yes, then a passive check is appropriate. If the answer to (2) is no, then a normal ability check is likely a better fit.

Well yeah, that is what it is. It seems to me that a well executed illusion has no counter if you don't use passive investigation. Let me use an example:

An enemy party is holding a noble hostage in his estate. The party consists of two rogues, a wizard, a barbarian, and the leader. The leader, a fighter, says to the party, "Stay here and keep an eye on our hostage. I'm going to check on our sentries posted on the upper levels. Don't do anything until I tell you." The players have a party with an illusionist and gets word from the scout. The illusionist makes a minor illusion of the leaders voice saying "Everybody get up here, there's trouble."

Now there's a few different ways the DM can go about this:

1. The enemy party all rushes to action. The PCs rush to get the hostage out uncontested.

2. The party all makes investigation checks for the source of the sound, checked against the spell DC. The player could argue that the party had "No logical reason" to investigate the sound and they do have somewhat of a point since the leader did just say wait for my next order. Not to mention the enemies would not want to "waste action" investigating when they think they are immediately needed to deal with a threat.

I wouldn't have a problem with the "meta knowledge" solution of NPCs rolling against every player illusion. In fact it seems many DMs do this for stealth and disguises. This does have the effect of slowing the game down however.

3. The enemy wizard is on level with the PC and automatically detects the illusion due to the passive investigation. This creates a new dynamic of having to scout for wizards and high intelligence creatures when attempting illusion trickery. And that perfectly makes sense, those creatures are practiced in magic and should be better at detecting illusions even when they aren't expecting them.

Or:

While the goal of the player creating the illusion isn't stated outright, let's say it's to draw the enemy party away from the hostage. The approach is the use of minor illusion to create the voice of the enemy party's leader and have it call away the enemy party. At this point, the DM must decide whether the action is successful, unsuccessful, or has an uncertain outcome.

Though we're missing a lot of context on which to base this decision, let's say for whatever reason, the DM says the outcome is uncertain. The rules tell us that when an action like this has an uncertain outcome, we use ability checks (Basic Rules, page 58). Thus, it would seem reasonable for the DM to ask the wizard to make a Charisma (Deception) check or even an Intelligence (Deception) check with an appropriate DC, perhaps with advantage for using magic to aid in the ruse. On a success, the enemies are drawn away from the hostage for a short time, leaving an opening for the PCs. On a failure, the enemies stay put as they suspect something is up. Or if you like success at a cost for failed checks, then the enemy party is drawn away, but before the PCs can take advantage of the opening, they run smack dab into the enemy party's leader, setting up a new, dramatic challenge.

 

[Elredion]

This reveals what I find to be a common misapprehension of what passive checks are for. In my initial post, I quote the rules and what they tell us is that passive checks are for resolving uncertainty as to the outcome of a particular task that is being performed repeatedly. That task must be described by the player like any other action, though sure, it's probably a common and fairly safe assumption at the table that unless the players describe some other action that is sufficiently distracting, the characters are keeping watch for hidden threats (and thus their passive Perception scores might apply to noticing hidden monsters and traps).

Someone who hopes to have his or her character's passive Investigation score apply to resolving uncertainty in a repeated task similarly needs to describe what the character is doing (approach) and hopes to achieve (goal). That is so the DM can decide what, if any, rules apply and narrate the result of the adventurer's action (Basic Rules, page 3). The example of the barbarian is a good one: He is tapping everything with his maul (approach) so as to uncover illusions (goal). Here we have a character performing a task repeatedly and although outright success seems like it might be an appropriate ruling, a DM who finds the outcome is uncertain can now use the character's passive Investigation score to determine an outcome.

So the questions I think the DM should ask himself or herself when adjudicating the player's stated action for the character is: (1) Is this effort successful, unsuccessful, or uncertain? and (2) If uncertain, is the character performing a task repeatedly? If the answer to (2) is Yes, then a passive check is appropriate. If the answer to (2) is no, then a normal ability check is likely a better fit.



Or:

While the goal of the player creating the illusion isn't stated outright, let's say it's to draw the enemy party away from the hostage. The approach is the use of minor illusion to create the voice of the enemy party's leader and have it call away the enemy party. At this point, the DM must decide whether the action is successful, unsuccessful, or has an uncertain outcome.

Though we're missing a lot of context on which to base this decision, let's say for whatever reason, the DM says the outcome is uncertain. The rules tell us that when an action like this has an uncertain outcome, we use ability checks (Basic Rules, page 58). Thus, it would seem reasonable for the DM to ask the wizard to make a Charisma (Deception) check or even an Intelligence (Deception) check with an appropriate DC, perhaps with advantage for using magic to aid in the ruse. On a success, the enemies are drawn away from the hostage for a short time, leaving an opening for the PCs. On a failure, the enemies stay put as they suspect something is up. Or if you like success at a cost for failed checks, then the enemy party is drawn away, but before the PCs can take advantage of the opening, they run smack dab into the enemy party's leader, setting up a new, dramatic challenge.

Well said and informative post. It seems I have misunderstood the purpose of passive stats.

Just curious, what would be the DC of the Deception check in this scenario?

 

[CapnZapp]

The example of the barbarian is a good one: He is tapping everything with his maul (approach) so as to uncover illusions (goal). Here we have a character performing a task repeatedly and although outright success seems like it might be an appropriate ruling, a DM who finds the outcome is uncertain can now use the character's passive Investigation score to determine an outcome.

Well, not really.

To get any mileage out of a passive check, the assumption is that you have a high score.

A dim-witted barbarian (Int 8, no proficiency) will never find anything during his investigations if you use the passive score, even if the illusion is as easy to find as DC 10. If you allow him to roll, on the other hand, he will now find 45% of all these illusions (rolling 11 on his d20).

The controversy regarding passive checks is "but then he auto-spots every hiding monster" but remember this goes both ways.

Again, as the DM you need to use the passive check mechanism judiciously. You can't just use it always (the "the rules says so" camp) and you really aren't giving it a chance if you use it never (the "it's broken" camp).

The passive check mechanism only works if you use it when you the DM decide to.

It's an aid to speed up gameplay, not an excuse to stop making DM judgement calls.

 

[iserith]

Well said and informative post. It seems I have misunderstood the purpose of passive stats.

Just curious, what would be the DC of the Deception check in this scenario?

It could be anything - context at that moment in gameplay would tell if it's very easy, nearly impossible, or somewhere in between.

 

[iserith]

Well, not really.

To get any mileage out of a passive check, the assumption is that you have a high score.

A dim-witted barbarian (Int 8, no proficiency) will never find anything during his investigations if you use the passive score, even if the illusion is as easy to find as DC 10. If you allow him to roll, on the other hand, he will now find 45% of all these illusions (rolling 11 on his d20).

The controversy regarding passive checks is "but then he auto-spots every hiding monster" but remember this goes both ways.

Again, as the DM you need to use the passive check mechanism judiciously. You can't just use it always (the "the rules says so" camp) and you really aren't giving it a chance if you use it never (the "it's broken" camp).

The passive check mechanism only works if you use it when you the DM decide to.

It's an aid to speed up gameplay, not an excuse to stop making DM judgement calls.

Couple of things:

1. My explanation of using the mechanic is rife with DM judgment calls, including the bit you quoted which suggests it's reasonable for the barbarian to succeed outright without reference to a check, passive or otherwise, due to the stated goal and approach.

2. It's on the players to put their characters in the best fictional position to succeed. If you're sending the dimwit to investigate the surroundings for illusions, then you're already at a disadvantage if the DM finds the effort to have an uncertain outcome. Sending someone more suited to the task, helping the barbarian (Help action), or spending 10 times the amount of time it would normally take, for example, are ways to increase the odds of success.

 

[CapnZapp]

Couple of things:

1. My explanation of using the mechanic is rife with DM judgment calls, including the bit you quoted which suggests it's reasonable for the barbarian to succeed outright without reference to a check, passive or otherwise, due to the stated goal and approach.

2. It's on the players to put their characters in the best fictional position to succeed. If you're sending the dimwit to investigate the surroundings for illusions, then you're already at a disadvantage if the DM finds the effort to have an uncertain outcome. Sending someone more suited to the task, helping the barbarian (Help action), or spending 10 times the amount of time it would normally take, for example, are ways to increase the odds of success.

True dat, but remember, the main issue with passive checks is inflexible rules interpretations.

And so it's imo critical to spell things out.

By the way, I would definitely allow the dimwit Barbarian to strike out on his own to find illusions.

What I would not do, however, is to penalize him by always using passive checks.

If the eagle-eye Elf does the same, I would be more than happy to use passive checks to tell him "you find every single one of them".

I hope you see the real take-away here, Iserith. Something that I feel gets obscured by the talk about Hepl actions or (what appears to be) your addition of the 3E rule "Take Twenty":

Don't make a single decision to always or never use passive checks. This is not an area where your response as DM should be to check the rulebook "does it say to use active or passive checks?"

Passive checks is a tool in the DMs toolbox. Use it when YOU feel it's warranted, but only then.

 

[strider13x]

Well, not really.

To get any mileage out of a passive check, the assumption is that you have a high score.

A dim-witted barbarian (Int 8, no proficiency) will never find anything during his investigations if you use the passive score, even if the illusion is as easy to find as DC 10. If you allow him to roll, on the other hand, he will now find 45% of all these illusions (rolling 11 on his d20).

The controversy regarding passive checks is "but then he auto-spots every hiding monster" but remember this goes both ways.

Again, as the DM you need to use the passive check mechanism judiciously. You can't just use it always (the "the rules says so" camp) and you really aren't giving it a chance if you use it never (the "it's broken" camp).

The passive check mechanism only works if you use it when you the DM decide to.

It's an aid to speed up gameplay, not an excuse to stop making DM judgement calls.

Throwing in my 2cp on this example...

The Barbarian stated his goal and is focused on looking for illusions. He should gain advantage on his passive score (+5). But that focus will cost him, he is alerting the goblins in the other room because of all that incessant tapping!

 

[iserith]

True dat, but remember, the main issue with passive checks is inflexible rules interpretations.

And so it's imo critical to spell things out.

I'm not sure what you mean here. Passive checks come into play when the player is having his or her character perform a task repeatedly and the outcome is uncertain (according to the DM).

By the way, I would definitely allow the dimwit Barbarian to strike out on his own to find illusions.

As DM, so would I - I can't control what he does. As a player, I would suggest the wizard or rogue with the decent INT and training in Investigation go with him and help out.

What I would not do, however, is to penalize him by always using passive checks.

Use of the passive check mechanic depends on whether the character is performing a task repeatedly and the outcome is uncertain. If the character has a low Intelligence and no training in Investigation and still puts his or her character into the fictional position of being the one to suss out illusions while traveling the dungeon, as DM, I really don't see why I should protect the player from his or her own sub-par decisions.

If the eagle-eye Elf does the same, I would be more than happy to use passive checks to tell him "you find every single one of them".

If the elf has a good passive Investigation score and is performing the task of deducing what is real and what is illusory, me too (provided the outcome is uncertain, otherwise I don't need to reference the passive score).

I hope you see the real take-away here, Iserith. Something that I feel gets obscured by the talk about Hepl actions or (what appears to be) your addition of the 3E rule "Take Twenty":

See DMG page 237: "...assume that a character spending ten times the normalamount of time needed to complete a task automatically succeeds at that task."

Don't make a single decision to always or never use passive checks. This is not an area where your response as DM should be to check the rulebook "does it say to use active or passive checks?"

First, an ability check - passive or otherwise - is used when the DM is uncertain as to the outcome of the player's stated approach to the goal.

Second, it's only a passive check if the approach to the goal is being performed repeatedly.

It's a simple test to see which mechanic to use to resolve uncertainty here. If the DM is ruling consistently, then the players can plan their characters' actions accordingly. I'm not sure of the basis for your objection exactly, but I hope that clears up my position.