Magical Hack

[iTreeby]

Nystul's Magic Aura is a seemingly niche spell that is mostly used for hiding magic items, you can also make it permanent, which is neat for saving spell slots.

I recently re-read the spell and saw that it can be cast on creatures as well so, now I have a few questions about the RAW, RAI and how the playground thinks it should work.

1) nystul's can permanently make you appear to not be under the effect of spells, which would no sell a) detect magic and b) identify.

2)nystul's can make you immune to spells and magical effects that only affect humanoids (hold person, charm person, dominate person) a very strict reading might mean that you cannot be nourished by the create food and water spell

3) you can make a simulacrum of a golem (by making it detect as a humanoid)

4) a 6th level illusionist wizard can change a nystul's magic aura as an action (not sure if they can a) see it b) see it with detect magic or c) see it with detect magic while it is hiding itself from detect magic)

Please weigh in on these scenarios and mention other aspects of the spell I may have missed.

[Unoriginal]

1) nystul's can permanently make you appear to not be under the effect of spells, which would no sell a) detect magic and b) identify.

That's the main purpose of the spell, yes.



2)nystul's can make you immune to spells and magical effects that only affect humanoids (hold person, charm person, dominate person) a very strict reading might mean that you cannot be nourished by the create food and water spell

No.

Nystul's Magic Aura only affects the *perception* of the creature type, it doesn't change the *facts* of the creature type. As clearly stated by the spell's description.

Nystul's Magic Aura can confuse magic meant to detect that X is an humanoid, but it does not affect spells that only react to the nature of humanoids.

To use an analogy: if you use illusions to make a jeweler believe that the block of wood you have is actually a gold ingot, it does *not* mean that the jeweler can melt the block of wood and make an alloy out of it by mixing it with silver.

Nystul's Magic Aura can make the orc-detecting sword not perceive an orc approaching, but it cannot make the hurts-orcs-a-lot sword not hurt the orc a lot if they get hit by it.


3) you can make a simulacrum of a golem (by making it detect as a humanoid)

No. See above.

You could make a wizard believe the golem is an humanoid and as such a viable target for Simulacrum by tricking the detection methods of the wizard, but it would not *become* a viable target.



4) a 6th level illusionist wizard can change a nystul's magic aura as an action (not sure if they can a) see it b) see it with detect magic or c) see it with detect magic while it is hiding itself from detect magic)

They wouldn't be able to detect it with Detect Magic, but if they're aware of it they can change it.

[MrCharlie]

What Unoriginal said.

Although...How would illusory reality interact with nystrals magic aura? What even is the difference between a "real" magic aura and a "fake" one? I can see the extreme edge case interpretation being that Nystrals magic aura would impose reality on the illusion, and transform the creature into what it's aura is of, which is bonkers. Alternatively, it might make it so that a creature magically acted like what it's aura was an illusion of. In which case...It might work like OP is arguing?

[iTreeby]

That's the main purpose of the spell, yes.



No.

Nystul's Magic Aura only affects the *perception* of the creature type, it doesn't change the *facts* of the creature type. As clearly stated by the spell's description.

Nystul's Magic Aura can confuse magic meant to detect that X is an humanoid, but it does not affect spells that only react to the nature of humanoids.

To use an analogy: if you use illusions to make a jeweler believe that the block of wood you have is actually a gold ingot, it does *not* mean that the jeweler can melt the block of wood and make an alloy out of it by mixing it with silver.

Nystul's Magic Aura can make the orc-detecting sword not perceive an orc approaching, but it cannot make the hurts-orcs-a-lot sword not hurt the orc a lot if they get hit by it.



No. See above.

You could make a wizard believe the golem is an humanoid and as such a viable target for Simulacrum by tricking the detection methods of the wizard, but it would not *become* a viable target.



They wouldn't be able to detect it with Detect Magic, but if they're aware of it they can change it.

So you would say magic circle for example cannot be spoofed to affect a humanoid?

And you would also say that nystul's magic aura can be made permanent and then at some later point you could cast invisibility and you would not be visible to detect magic?

[Kvess]

I think I can see where the confusion is. The spell says "You change the way the target appears to Spells and magical Effects that detect creature types…"

The bolded text could be interpreted to mean it applies to spells or effects that care about a given creature’s type — Hold Person 'detects' whether it is being cast on a humanoid, and decided not to function if it is cast on the wrong creature.

This reading makes a certain intuitive sense, but it gives Hold Person agency it does not have or need. This would be like saying that a car decides not to run if it does not have gasoline. Similar to a car with an empty tank, a spell like Hold Person just fails if it does not have a valid target. An invalid target disguised as a valid target does not qualify. Like a gallon of Pepsi in a gas can, a vampire disguised with a person’s aura is not persony enough for the spell to take hold.

That said, an Improved Magic Aura which would allow a creature to change its type for the purpose of triggering spells, effects and magic items would be a very interesting homebrew spell.

[ftafp]

What Unoriginal said.

Although...How would illusory reality interact with nystrals magic aura? What even is the difference between a "real" magic aura and a "fake" one? I can see the extreme edge case interpretation being that Nystrals magic aura would impose reality on the illusion, and transform the creature into what it's aura is of, which is bonkers. Alternatively, it might make it so that a creature magically acted like what it's aura was an illusion of. In which case...It might work like OP is arguing?

This is a cool idea, but unfortunately Illusory Reality is limited to making an illusory nonmagic object real. You can't make a subjective property real

[JoeJ]

So you would say magic circle for example cannot be spoofed to affect a humanoid?

The description of magic circle says that it affects creatures that are celestials, elements, fey, fiends, or undead, not creatures that detect as those things. IOW, it triggers on what is real, not what is perceived.

[Greywander]

Since playable undead is something that I've explored before, and with undead typically being treated as evil, Nystul's Magic Aura was a solution to evading attempts to detect that the player is undead. However, as others have said, it doesn't make me not undead. If I get hit by a paladin smite, I still take that extra damage. If a cleric uses Turn Undead in my general area, I'll still need to save or flee. But what it does do is make it so I don't have to worry about Detect Evil and Good or Divine Sense, so I don't get shanked by a bunch of clerics in a dark alley.

Think of it like Disguise Self, in the sense that it wraps an illusion around the creature or object to change its appearance, while the underlying creature or object is the same as they were before. Alter Self will actually change your form, but Disguise Self only hides it. Magic Aura is the same; it merely hides the underlying aura and creates a fake aura to broadcast instead.

[MrCharlie]

This is a cool idea, but unfortunately Illusory Reality is limited to making an illusory nonmagic object real. You can't make a subjective property real
We could really get into the magical metaphysics of if an "aura" is an object here, so I'll just concede that this is probably right but that I could imagine interpreting otherwise.

[Segev]

We could really get into the magical metaphysics of if an "aura" is an object here, so I'll just concede that this is probably right but that I could imagine interpreting otherwise.
Just being pedantic at this point since you’re not arguing, but an aura would qualify as a phenomenon, rather than an object. (See Silent Image for an example of a spell that calls out the categories of “creature,” “object,” and “phenomenon” as distinct.)

[ftafp]

Can I be frank? Nystul's Magic Aura is a spell that often ends up on the radar of more ambitious theoretical mini-maxers because its vague spell description potentially opens the doors for some truly broken combos, but ultimately it's an illusion spell and it's hard to justify many of the uses people come up with for it. This is far more apparent when you realize that the secret to breaking Nystul's Magic Aura doesn't rely on the creature feature but on doing what illusion spells do best: con-artistry.

Creation for example is potentially a great spell to make money with if you're creative enough to circumvent its limits, but for high-price transactions it falls short due to the fact that any sane salesman would use detect magic to determine if the expensive treasure they're buying is conjured. Magic Aura lets you hide its aura of conjuration, and not only that but also the aura of Distort Value, which doubles the perceived value of the objects you cast it on. With those three combined, you can sell an illusory chest of spyglasses for 300,005gp, leave the buyer none the wiser and have 12 hours to skip town and make off with the cash. It's useful

[Unoriginal]

So you would say magic circle for example cannot be spoofed to affect a humanoid?

Indeed.



And you would also say that nystul's magic aura can be made permanent and then at some later point you could cast invisibility and you would not be visible to detect magic?

I would say that if you apply new magic on yourself, you'll need a new Nystul's Magic Aura to hide it.

[kazaryu]

So you would say magic circle for example cannot be spoofed to affect a humanoid?

And you would also say that nystul's magic aura can be made permanent and then at some later point you could cast invisibility and you would not be visible to detect magic?

you already can't 'see' a person that is invisible with detect magic. the most you can get is a sense that magic is present. in order to 'see' the aura and determines its school the creature needs to explicitly be visible. which makes detect magic pretty ****ty in terms of finding an invisible person once the party starts acquiring magic items. since you'd have no way to distinguish the sense of 'there's magic' coming off of an invisible creature as opposed to the magic items in the area.

[Keravath]

In terms of RAI, I likely agree with Unoriginal and the rest - most of these shouldn't work - however, in terms of RAW, some of them likely would.

Here is the key sections from Nystul's

"You place an illusion on a creature or an object you touch so that divination spells reveal false information about it."

"Mask. You change the way the target appears to spells and magical effects that detect creature types, such as a paladin's Divine Sense or the trigger of a symbol spell. You choose a creature type and other spells and magical effects treat the target as if it were a creature of that type or of that alignment."

The first sentence makes it sound like the Aura will only affect divination spells. However, the text for Mask specifically states that "You change the way the target appears to spells and magical effects that detect creature types" and "magical effects treat the target as if it were a creature of that type or of that alignment."

The first reaction is to think perhaps that it is divination spells that treat the target as if it were that creature or alignment. However, Divine Sense is not a spell and Symbol is an abjuration spell and not a divination one. Clearly reading the text of the mask ability and the explicit examples, the RAW allows Nystul's magical aura to change the perceived creature type for the purposes of targeting any other spells and effects (not just divination spells). That is RAW and it is very explicit in both text and example.

So to answer the OP.

1) Yes. This is the basic function of the spell.

"2)nystul's can make you immune to spells and magical effects that only affect humanoids (hold person, charm person, dominate person) a very strict reading might mean that you cannot be nourished by the create food and water spell"

Yes, if you cast Nystul's magic aura on yourself and change your creature type to NOT be humanoid then these spells which target humanoids can not target you since the spells require a humanoid target and the mask ability explicitly sets the creature type to something else for ALL spells not just divination ones.

"3) you can make a simulacrum of a golem (by making it detect as a humanoid)"

Yes. You could use the aura to change the target type to beast or humanoid from construct and could then cast simulacrum on the creature because from the spell point of view it is now a valid target.

"4) a 6th level illusionist wizard can change a nystul's magic aura as an action (not sure if they can a) see it b) see it with detect magic or c) see it with detect magic while it is hiding itself from detect magic)"

No in most cases - DM call if detect magic is in use. Malleable illusions doesn't apply to Nystul's Magic Aura since the spell produces nothing visible. The illusionist can't see the illusion. Nystul's Magic Aura changes the perceived creature type or hides a property of an item from other spells but there is nothing to see and thus nothing for the illusionist to change using Malleable Illusions. Even if an illusionist was using detect magic they still don't see the illusion. Detect magic explicitly uses the term sense though sensing something magical can give you the ability to see the aura of magic. If there is no aura of magic then there is nothing to see. It would be a DM call whether an illusionist using detect magic would be able to change the aura of a magic effect caused by a Nystul's Magic Aura that they previously cast.



Nystul's Magic Aura is a seemingly niche spell that is mostly used for hiding magic items, you can also make it permanent, which is neat for saving spell slots.

I recently re-read the spell and saw that it can be cast on creatures as well so, now I have a few questions about the RAW, RAI and how the playground thinks it should work.

1) nystul's can permanently make you appear to not be under the effect of spells, which would no sell a) detect magic and b) identify.

2)nystul's can make you immune to spells and magical effects that only affect humanoids (hold person, charm person, dominate person) a very strict reading might mean that you cannot be nourished by the create food and water spell

3) you can make a simulacrum of a golem (by making it detect as a humanoid)

4) a 6th level illusionist wizard can change a nystul's magic aura as an action (not sure if they can a) see it b) see it with detect magic or c) see it with detect magic while it is hiding itself from detect magic)

Please weigh in on these scenarios and mention other aspects of the spell I may have missed.

[Keravath]

The description of magic circle says that it affects creatures that are celestials, elements, fey, fiends, or undead, not creatures that detect as those things. IOW, it triggers on what is real, not what is perceived.

The description of Nystul's says:

"Mask. You change the way the target appears to spells and magical effects that detect creature types, such as a paladin's Divine Sense or the trigger of a symbol spell. You choose a creature type and other spells and magical effects treat the target as if it ere a creature of that type or of that alignment.

Is Magic Circle a spell? Yes
Does Magic Circle detect creature types? Yes - since it only functions on specific creature types
"Choose one or more of the following types of creatures: celestials, elementals, fey, fiends, or undead. The circle affects a creature of the chosen type in the following ways:"

Nystul's Magic Aura using the Mask feature explicitly changes the creature type for the casting of "other spells". Since Magic Circle is another spell that detects creature types to function then Nystul's Magic Aura can be used to change the creature type to be something that would not be targeted by a magic circle spell.

RAW, it would appear to work unless I am missing something. Is it RAI? I don't think so. Would I allow it? Probably not in most cases but I'd have to think about it. There are some situations where certain creatures would obviously pay others to cast it on them if it had such a significant effect (e.g. intelligent undead like vampires having Nystuls magic aura cast on them so that they could not be turned. Channel Divinity: Turn Undead is a magical effect that targets undead creatures for example).

[Segev]

The last line in the section quoted does, indeed, seem to say that spells and effects treat the target of Nystule’s magic aura as a creature of the type it disguised their aura to be. Which is amazingly powerful. You can now use Hold Person on anything you can hit with Nystule’s Magic Aura!

[JackPhoenix]

Can I be frank? Nystul's Magic Aura is a spell that often ends up on the radar of more ambitious theoretical mini-maxers because its vague spell description potentially opens the doors for some truly broken combos, but ultimately it's an illusion spell and it's hard to justify many of the uses people come up with for it. This is far more apparent when you realize that the secret to breaking Nystul's Magic Aura doesn't rely on the creature feature but on doing what illusion spells do best: con-artistry.

Creation for example is potentially a great spell to make money with if you're creative enough to circumvent its limits, but for high-price transactions it falls short due to the fact that any sane salesman would use detect magic to determine if the expensive treasure they're buying is conjured. Magic Aura lets you hide its aura of conjuration, and not only that but also the aura of Distort Value, which doubles the perceived value of the objects you cast it on. With those three combined, you can sell an illusory chest of spyglasses for 300,005gp, leave the buyer none the wiser and have 12 hours to skip town and make off with the cash. It's useful

That assumes that a) someone has 300 005 gp available b) that someone wants to buy a chest of spyglasses instead of something useful and c) he'll pay on the spot instead of letting you wait for a day while the goods is in safe deposit to make sure the deal is legit.

[Darzil]

I think the way to think about the Magic Circle for example is:

Does the magic circle detect a creature, and then effect them if they match it's criteria.
Or does the magic circle just produce an effect that only affects a target matching it's criteria.

I'd rule the latter, or spells become sentient!

[iTreeby]

I would say that if you apply new magic on yourself, you'll need a new Nystul's Magic Aura to hide it.

I've really appreciated your opinion, do you have a raw reason for this particular case?

Thanks to everyone for their input.

[JoeJ]

I think the way to think about the Magic Circle for example is:

Does the magic circle detect a creature, and then effect them if they match it's criteria.
Or does the magic circle just produce an effect that only affects a target matching it's criteria.

I'd rule the latter, or spells become sentient!

I see it that way too. Fire doesn't "detect" whether an object is flammable, it just ignites everything that is. I'd say Magic Circle works the same way.

[MrCharlie]

In terms of RAI, I likely agree with Unoriginal and the rest - most of these shouldn't work - however, in terms of RAW, some of them likely would.

"Mask. You change the way the target appears to spells and magical effects that detect creature types, such as a paladin's Divine Sense or the trigger of a symbol spell. You choose a creature type and other spells and magical effects treat the target as if it were a creature of that type or of that alignment."

The first sentence makes it sound like the Aura will only affect divination spells. However, the text for Mask specifically states that "You change the way the target appears to spells and magical effects that detect creature types" and "magical effects treat the target as if it were a creature of that type or of that alignment."

The first reaction is to think perhaps that it is divination spells that treat the target as if it were that creature or alignment. However, Divine Sense is not a spell and Symbol is an abjuration spell and not a divination one. Clearly reading the text of the mask ability and the explicit examples, the RAW allows Nystul's magical aura to change the perceived creature type for the purposes of targeting any other spells and effects (not just divination spells). That is RAW and it is very explicit in both text and example.
I've had this conversation before, in different context.

Strictly speaking, this isn't wrong. It's a valid interpretation. But it requires reading the second sentence of mask as separate from the rest of the text. I.E. it requires saying that the first sentence is unconnected to the second. The first sentence clearly limits it to detection, and the second enumerates how that detection is modified.

This isn't a RAI versus RAW difference, this is a question of grammar. It is entirely correct to say that you can read both sentences as distinct, and entirely wrong to say this makes it RAW. It makes it interpretive. And the most grammatically consistent interpretation is that the bolded sentence is modifying the first sentence, not a separate thought, and thus the entire effect only works on detection effects.

Now, you might ask why Symbol is listed, but symbol is determining what it attempts to target, not what it targets when triggered. I.E. symbol targets everyone in the AOE, but only triggers for people of a type you specify. Hence, there is a part of symbol which detects creature types, as separate from the part that targets creatures.

Divination spells are not at issue here. Whether a spell or magical effects detects is. The first sentence limits the effect to detection, the sentence elaborates how the first sentence works. The other interpretation is not consistent, though I won't go as far as to say it's not a valid interpretation of RAW. It's not the favored or logical interpretation of the RAW though.

[Segev]

I've had this conversation before, in different context.

Strictly speaking, this isn't wrong. It's a valid interpretation. But it requires reading the second sentence of mask as separate from the rest of the text. I.E. it requires saying that the first sentence is unconnected to the second. The first sentence clearly limits it to detection, and the second enumerates how that detection is modified.

This isn't a RAI versus RAW difference, this is a question of grammar. It is entirely correct to say that you can read both sentences as distinct, and entirely wrong to say this makes it RAW. It makes it interpretive. And the most grammatically consistent interpretation is that the bolded sentence is modifying the first sentence, not a separate thought, and thus the entire effect only works on detection effects.

Now, you might ask why Symbol is listed, but symbol is determining what it attempts to target, not what it targets when triggered. I.E. symbol targets everyone in the AOE, but only triggers for people of a type you specify. Hence, there is a part of symbol which detects creature types, as separate from the part that targets creatures.

Divination spells are not at issue here. Whether a spell or magical effects detects is. The first sentence limits the effect to detection, the sentence elaborates how the first sentence works. The other interpretation is not consistent, though I won't go as far as to say it's not a valid interpretation of RAW. It's not the favored or logical interpretation of the RAW though.

I would argue that, if the intent was to connect the first and second sentences, then the second sentence should read something like, "You choose a creature type, and such spells and magical effects...," or, "You choose a creature type, and spells and other spells and magical effects detect the target...."

[Keravath]

I've had this conversation before, in different context.

Strictly speaking, this isn't wrong. It's a valid interpretation. But it requires reading the second sentence of mask as separate from the rest of the text. I.E. it requires saying that the first sentence is unconnected to the second. The first sentence clearly limits it to detection, and the second enumerates how that detection is modified.

This isn't a RAI versus RAW difference, this is a question of grammar. It is entirely correct to say that you can read both sentences as distinct, and entirely wrong to say this makes it RAW. It makes it interpretive. And the most grammatically consistent interpretation is that the bolded sentence is modifying the first sentence, not a separate thought, and thus the entire effect only works on detection effects.

Now, you might ask why Symbol is listed, but symbol is determining what it attempts to target, not what it targets when triggered. I.E. symbol targets everyone in the AOE, but only triggers for people of a type you specify. Hence, there is a part of symbol which detects creature types, as separate from the part that targets creatures.

Divination spells are not at issue here. Whether a spell or magical effects detects is. The first sentence limits the effect to detection, the sentence elaborates how the first sentence works. The other interpretation is not consistent, though I won't go as far as to say it's not a valid interpretation of RAW. It's not the favored or logical interpretation of the RAW though.

I can understand your interpretation. However, it hinges on a particular interpretation of what it means for a spell to "detect" something. The symbol spell for example never uses the term detect. You simply describe what triggers it and creature type is one of the possible options. Similarly, you can cast magic circle and specify one of a number of possible creature types that would be affected. Some spells have a fixed creature type they affect like hold person affecting only humanoids.

None of these spells indicate the mechanism they use to "detect" the type of creature that the spell is trying to affect. Why would a symbol spell cast to affect a fey creature be fooled by a Nystuls aura that changes it to a humanoid while a Magic Circle spell with a fey chosen out of the list of the creatures to be affected NOT be affected by the Nystuls Aura spell? Both spells can use creature type for targeting those affected. Similarly, hold person, although it only has one choice for humanoids, also doesn't indicate how the magic decides a valid target.

The full text of mask says "Mask. You change the way the target appears to spells and magical effects that detect creature types, such as a paladin's Divine Sense or the trigger of a symbol spell. You choose a creature type and other spells and magical effects treat the target as if it were a creature of that type or of that alignment.

I'd argue that one valid interpretation is that every spell which has a limitation on creature types that it can affect must detect the type of creature it is cast on to see whether it is takes effect or not. Thus both sentences could and would apply to every spell or magical effect that only works on specific creature types since every one of these magical effects must be able to detect the creature type in order to determine whether the effect can occur or not.

On the other hand, I can certainly see the interpretation of you and others that a spell doesn't need to "divine" the nature of the target to affect it - it just needs to check the actual creature type when cast and although Nystul's changes what type a creature appears to be for spells and magical effects, it doesn't actually change what the creature is. However, I don't really see why Symbol would be affected and none of the other spells that have limited creature types they affect would not.

Symbol, Glyph of Warding, Magic Circle - all use similar wording in selecting a limited set of creature types that could be affected by the spells. The only difference between these and hold person is that hold person has a fixed creature type - however, if one assumes that valid target selection is part of the spell targeting process (as it is explicitly with Symbol, Glyph of Warding and Magic Circle then hold person would fail to target a creature that is disguised as a non-humanoid) the Nystuls magic aura could be used to change perceived creature type for targeting the spell since creature type is detected by the spell prior to resolution. On the other hand, if a DM prefers that creature type is determined at spell resolution then it is determined when the spell is resolved and then doesn't have any affect on creatures of an inappropriate type (but then you get into an issue where you have to trigger the spell first and check for a valid target afterward).

So, I could see it going either way and both being valid interpretations leaving it up to the DM running the game to decide which way they want to run it.

[Darzil]

Symbol, Glyph of Warding, Magic Circle - all use similar wording in selecting a limited set of creature types that could be affected by the spells. The only difference between these and hold person is that hold person has a fixed creature type - however, if one assumes that valid target selection is part of the spell targeting process (as it is explicitly with Symbol, Glyph of Warding and Magic Circle then hold person would fail to target a creature that is disguised as a non-humanoid) the Nystuls magic aura could be used to change perceived creature type for targeting the spell since creature type is detected by the spell prior to resolution. On the other hand, if a DM prefers that creature type is determined at spell resolution then it is determined when the spell is resolved and then doesn't have any affect on creatures of an inappropriate type (but then you get into an issue where you have to trigger the spell first and check for a valid target afterward).

I'd rule that the aura would fool Symbol and Glyph (depending on their trigger), as they are triggering one off spells when something meets the requirements of what they can effect.

Magic Circle I'd rule it wouldn't, that is just an effect that is there, and continues afterwards. It is just a constant effect (for the duration) that affects (or doesn't) anything trying to pass through it.

[MrCharlie]

I can understand your interpretation. However, it hinges on a particular interpretation of what it means for a spell to "detect" something. The symbol spell for example never uses the term detect. You simply describe what triggers it and creature type is one of the possible options. Similarly, you can cast magic circle and specify one of a number of possible creature types that would be affected. Some spells have a fixed creature type they affect like hold person affecting only humanoids.

None of these spells indicate the mechanism they use to "detect" the type of creature that the spell is trying to affect. Why would a symbol spell cast to affect a fey creature be fooled by a Nystuls aura that changes it to a humanoid while a Magic Circle spell with a fey chosen out of the list of the creatures to be affected NOT be affected by the Nystuls Aura spell? Both spells can use creature type for targeting those affected. Similarly, hold person, although it only has one choice for humanoids, also doesn't indicate how the magic decides a valid target.

The full text of mask says "Mask. You change the way the target appears to spells and magical effects that detect creature types, such as a paladin's Divine Sense or the trigger of a symbol spell. You choose a creature type and other spells and magical effects treat the target as if it were a creature of that type or of that alignment.

I'd argue that one valid interpretation is that every spell which has a limitation on creature types that it can affect must detect the type of creature it is cast on to see whether it is takes effect or not. Thus both sentences could and would apply to every spell or magical effect that only works on specific creature types since every one of these magical effects must be able to detect the creature type in order to determine whether the effect can occur or not.

On the other hand, I can certainly see the interpretation of you and others that a spell doesn't need to "divine" the nature of the target to affect it - it just needs to check the actual creature type when cast and although Nystul's changes what type a creature appears to be for spells and magical effects, it doesn't actually change what the creature is. However, I don't really see why Symbol would be affected and none of the other spells that have limited creature types they affect would not.

Symbol, Glyph of Warding, Magic Circle - all use similar wording in selecting a limited set of creature types that could be affected by the spells. The only difference between these and hold person is that hold person has a fixed creature type - however, if one assumes that valid target selection is part of the spell targeting process (as it is explicitly with Symbol, Glyph of Warding and Magic Circle then hold person would fail to target a creature that is disguised as a non-humanoid) the Nystuls magic aura could be used to change perceived creature type for targeting the spell since creature type is detected by the spell prior to resolution. On the other hand, if a DM prefers that creature type is determined at spell resolution then it is determined when the spell is resolved and then doesn't have any affect on creatures of an inappropriate type (but then you get into an issue where you have to trigger the spell first and check for a valid target afterward).

So, I could see it going either way and both being valid interpretations leaving it up to the DM running the game to decide which way they want to run it.
No, symbol has one other very important distinction shared with glyph of warding. It separates a trigger from a target. For either spell both can be the same thing-what triggers the glyph can be the target-but they don't have to be. Because the spell is defining a set of triggers, and then explaining how it targets creatures based on being triggered, it's got a clear distinction that separates it from Hold Person (and magic circle).

The "detection" capabilities of the spell are implicit in what triggering is. Something needs to be able to detect the triggering condition for it to be triggered. We can get into philosophy about if it's appropriate for an inanimate object or phenomenon to be "detecting" anything, but to be completely honest that applies to every spell.

Basically, the text specifically including symbol clearly extends (or intends to extend) the scope of magic aura to "detection" via trigger conditions. What you're trying to do is extend it past trigger conditions and into targeting, which is not in any way implicit with the inclusion of triggered spells. There is a distinction there, implicit in the text of glyph of warding and symbol, between what triggers the spells activation and the targets of the spell afterwords.

But there is another solution here-to simply say that the spell is inconsistent. That symbol is not covered and that it should not have been included. And this makes more sense than saying that hold person is, as long as you read those two sentences as connected-that the second sentence is still constrained by the rules of the first.

It's still a valid interpretation otherwise, but it requires that you interpret the second sentence in a way that contradicts the wording of the first. Because, quite simply, detection is not the same thing as being a valid target for a spell, and hold person is not "detecting" anything.

[kingcheesepants]

The last line in the section quoted does, indeed, seem to say that spells and effects treat the target of Nystule’s magic aura as a creature of the type it disguised their aura to be. Which is amazingly powerful. You can now use Hold Person on anything you can hit with Nystule’s Magic Aura!

Absolutely, anything that you can hit with Nystul's magic aura. Who can you hit with the spell? Let's look at the description again.
You place an illusion on a creature or an object you touch so that divination spells reveal false information about it. The target can be a willing creature or an object that isn’t being carried or worn by another creature.

I doubt many enemies are gonna be willing for you to cast some spell on them to make them easier to hit. But if you can trick them into accepting it than all the power to ya.

[Phhase]

Oh boy, I once had a brain blast about exactly this type of situation: Using Nystul's to trick the Banishment spell into sending a creature another plane, potentially permanently, by altering its perceived creature type. What complicates things is that Banishment is capable of targeting and affecting enemies that are already on their home plane, meaning it has some ability to choose where a creature ends up - there is potential for the inverse, that an extraplanar entity could use the spell to prevent Banishment from sending it back to its home plane permanently.

[Maelynn]

I've read this thread with a bit of confusion. Correct me if I'm wrong, but it seems that a very important part of the spell is overlooked: the very first sentence of it.

"You place an illusion on a creature or an object you touch so that divination spells reveal false information about it."

There. That's it. That's the effect the spell creates. Everything described under False Aura and Mask only serve to go into more detail about that particular aspect of the spell, but they still adhere to the main working of the spell: reveal false information to divination spells. They can't possibly do more than what the initial description of the spell states.

Hold person isn't a divination spell. Magic Circle isn't a divination spell. Symbol isn't a divination spell. They'd never work differently on a character affected by Nystul's Magic Aura, because this spell only influences divination spells.

[JackPhoenix]

I've read this thread with a bit of confusion. Correct me if I'm wrong, but it seems that a very important part of the spell is overlooked: the very first sentence of it.

"You place an illusion on a creature or an object you touch so that divination spells reveal false information about it."

There. That's it. That's the effect the spell creates. Everything described under False Aura and Mask only serve to go into more detail about that particular aspect of the spell, but they still adhere to the main working of the spell: reveal false information to divination spells. They can't possibly do more than what the initial description of the spell states.

Hold person isn't a divination spell. Magic Circle isn't a divination spell. Symbol isn't a divination spell. They'd never work differently on a character affected by Nystul's Magic Aura, because this spell only influences divination spells.

Mask option of NMA specifically says it interferes with Symbol. One thing to note that Symbol has two components: one is the trigger, and other is the choosen effect. The trigger allows you to choose what creatures will or will not trigger the spell, but the effect targets everyone in the AoE once the spell is triggered.

[Maelynn]

Mask option of NMA specifically says it interferes with Symbol. One thing to note that Symbol has two components: one is the trigger, and other is the choosen effect. The trigger allows you to choose what creatures will or will not trigger the spell, but the effect targets everyone in the AoE once the spell is triggered.

Ah, thank you for that correction. In a "today I learnt" moment, I always thought the PHB had both spells and abilities capitalised - only now that I reread that part do I realise spells are lowercase and cursive.

This thread is starting to make some more sense now. Unlike the spell. :p

[Keravath]

Ah, thank you for that correction. In a "today I learnt" moment, I always thought the PHB had both spells and abilities capitalised - only now that I reread that part do I realise spells are lowercase and cursive.

This thread is starting to make some more sense now. Unlike the spell. :p

Yep. Divine sense isn't a spell and Symbol is an abjuration spell so the aura doesn't just work on "divination spells".

The interpretation and use of the Mask ability is then up to the DM depending on how the specific individual decides to read the description. There is no one correct answer to that, though some folks seem to have strong opinions, and as a result, how the spell works in a specific DMs game is up to that DM.