Disbelieving Illusory Disguise

Magic with the illusion trait creates false sensory stimuli. Sometimes illusions allow creatures a chance to disbelieve the spell, which lets the creature ignore the spell if it succeeds at doing so. This usually happens when a creature Seeks, Interacts, or otherwise spends actions to engage with the illusion, comparing the result of its Perception check (or another check or save the GM chooses) to the caster’s spell DC. Mental illusions typically provide rules in the spell’s description for disbelieving the effect (usually via a Will save).

If a creature engages with an illusion in a way that would prove it’s not what it seems, the creature might know that an illusion is present, but it still can’t ignore the illusion without successfully disbelieving it. Disbelieving a visual illusion makes it and those things it blocks seem hazy and indistinct, which might block vision enough to leave the other side concealed.

You create an illusion that causes the target to appear as another creature of the same body shape, and with roughly similar height (within 6 inches) and weight (within 50 pounds). The disguise is typically good enough to hide their identity, but not to impersonate a specific individual. The spell changes their appearance and voice, but not mannerisms. You can change the appearance of its clothing and worn items, such as making its armor look like a dress. Held items are unaffected, and any worn item removed from the creature returns to its true appearance.

Casting illusory disguise counts as setting up a disguise for the Impersonate use of Deception; it ignores any circumstance penalties the target might take for disguising itself as a dissimilar creature, gives a +4 status bonus to Deception checks to prevent others from seeing through the disguise, and lets the target add its level to such Deception checks even if untrained. You can Dismiss this spell.

Trying to future proof here, because one of my players is planning on running a character that will be using Illusory Disguise a lot. And I wanted to determine if I was accurate in my understanding:

Can Illusory Disguise be disbelieved, and if yes, what triggers disbelief? My current impression is that an NPC can only uncover the disguise by passing a Perception check against their Deception DC, and is not capable of disbelieving the illusion as the spell does not mention the ability to disbelieve. But I would like to know whether or not I am correct in this assumption.

If an Illusory Disguise could be disbelieved, what sort of parameters would the illusion have to have for an NPC to ignore it.

sure it can, if a target interacts with the illusion in a way that makes the illusion improbable, it is a cause for rolling to disbelief.

as a simple example, Illusory disguise is only Visual. So any other sense like Scent can potentially alert someone that something is not right.

Other stuff can be as simple as using an effect that should do one thing vs you, and it does something different than expected. Say, you have Void healing and someone casts 3 action heal.

At the fundamental level, any interaction that can make the target go "hmmm that's not right!" may be cause to disbelief.

what triggers disbelief?

It is highly GM dependant. It occurs when when a creature Seeks, Interacts, or otherwise spends actions to engage with the illusion

One would likely need good Deception & Charisma to help with this, yet then cut themselves off from being the face because focused interactions with NPCs could grant them a roll which one would try to avoid. Seems like a waste of investment (that is, if disguised as a norm).

One thing to note is that the game math is expecting for opposed checks to be rolled once. Generally a PC has somewhere between a 40% - 65% chance of succeeding at any particular roll that they have to make. If the number of rolls needed is increased, the chances that all of the rolls succeed drops exponentially.

So if a PC has a 50% chance of succeeding at the Impersonate check, and the NPC that is being duped has a 50% chance of succeeding at a Will save to disbelieve the illusion, then there is only a 25% chance of that interaction going the way the PC wants. If they have to encounter two other people along the way and do both checks for each of them as well, then the chance of success is 1.5%. One of the three of them is going to notice something.

One thing to note is that the game math is expecting for opposed checks to be rolled once.

In the broader case than just illusions, is there a good discussion of this somewhere?

Finoan wrote:

One thing to note is that the game math is expecting for opposed checks to be rolled once.

In the broader case than just illusions, is there a good discussion of this somewhere?

Do you need more than the math itself as evidence?

People complained about Ray of Enfeeblement because it had both a spell attack roll and a saving throw by the target. So much so that Enfeeble in PC2 doesn't have that - saving throw only.

IMO: This is one of the byproducts of the power ceiling change from PF1 to PF2. In PF1 you could get away with multiple rolls because it was assumed that the players could build their characters to trivialize the necessary rolls. If the probability of each roll succeeding is 90%, then three rolls still has a 73% chance of overall success.

PF2 doesn't allow that. If the best build options give you a 60% chance of success, then three rolls needed gives you 22% chance overall.

If you do want to run a more complicated scene where multiple rolls are needed for success, the way to do that in PF2 is with a Victory Point skill challenge.

The reason is that with the VP system, you don't require all of the rolls to be successful in order for the scene overall to be a success. It bypasses the exponential decrease in multiple required rolls by not having all of them be required successes.

Gortle wrote:

Finoan wrote:

One thing to note is that the game math is expecting for opposed checks to be rolled once.

In the broader case than just illusions, is there a good discussion of this somewhere?

Do you need more than the math itself as evidence?

People complained about Ray of Enfeeblement because it had both a spell attack roll and a saving throw by the target. So much so that Enfeeble in PC2 doesn't have that - saving throw only.

IMO: This is one of the byproducts of the power ceiling change from PF1 to PF2. In PF1 you could get away with multiple rolls because it was assumed that the players could build their characters to trivialize the necessary rolls. If the probability of each roll succeeding is 90%, then three rolls still has a 73% chance of overall success.

PF2 doesn't allow that. If the best build options give you a 60% chance of success, then three rolls needed gives you 22% chance overall.

That's far from the only time it happens though.

Most deceptive tactics work like that. You first need to succeed, and if for some reason (either due to duty or due to your decisions) an enemy tries to thwart you he also gets a countercheck.

Things like concealing an object, which has a secondary roll if someone actively searches you instead of casually looking at you.
Or even plain hiding, when if suspicious someone can Seek (after you have already passed your check to hide).

Not generally, no. Illusory Disguise has no section discussing disbelief rules. It provides a disguise bonus, and the disguise rules are how to "beat" the spell.

Compare with Illusory Object, which says "Any creature that touches the image or uses the Seek action to examine it can attempt to disbelieve your illusion."

If an interaction is impossible, someone can still learn that a creature is using an illusory disguise, but they still need to repeatedly seek to beat the DC of the disguise if they want to figure out who the person really is- or keep track of them until it wears off, of course.