Detect Magic Vs Illusions (and casters in general)

[ironkid]

Detect magic reads:

"For the duration, you sense the presence of magic within 30 feet of you. If you sense magic in this way, you can use your action to see a faint aura around any visible creature or object in the area that bears magic, and you learn its school of magic, if any."

:vaarsuvius: 1) If I detect disguise self, the caster of detect magic is seeing the illusion covering me, not me. So she wouldn't detect any magic, is that correct? (I don't think the illusion counts as an object)

:vaarsuvius: 2) By the same logic, if I cast mirror image and the opponent has detect magic active, she wouldn't detect magic in any of my images... BUT if I'm wearing, say, a magic armor, she would detect its magic, so the illusions would be useless; is that correct.

:vaarsuvius: 3) Let's say I don't have any magic cast on me and no magic items. Even if I have plenty of spell slotsspell slots, I wouldn't radiate magic, right? What if I'm a warlock with clearly supernatural invocations (say, devil's sight)? What about familiars, do they radiate magic? I think they're BROUGHT by conjuration magic by an instantaneous efect, so they wouldn't radiate magic as they are...

Any comments would be much appreciated.

[Greywander]

:vaarsuvius: 1) If I detect disguise self, the caster of detect magic is seeing the illusion covering me, not me. So she wouldn't detect any magic, is that correct? (I don't think the illusion counts as an object)
I think this still counts as seeing the creature (otherwise, you could, say, take the Hide action because you're not "visible", which is silly). The caster of Detect Magic would see that the creature was being affected by an illusion spell, but they wouldn't know which one.

In general, I would also think that if the caster of Detect Magic sees an illusion, they would see it as an object being affected by an illusion spell. This wouldn't necessarily mean the object itself is an illusion, though.


:vaarsuvius: 2) By the same logic, if I cast mirror image and the opponent has detect magic active, she wouldn't detect magic in any of my images... BUT if I'm wearing, say, a magic armor, she would detect its magic, so the illusions would be useless; is that correct.
As above, I would think they'd see that you and your copies are being affected by an illusion spell (and yes, you cast the spell on yourself, so you are being affected by an illusion spell, even if there isn't an illusion on yourself). I suspect that you are correct that if you are carrying any magic items then Detect Magic would see those on the real you, but not on your illusory doubles. So Detect Magic might be able to defeat Mirror Image.


:vaarsuvius: 3) Let's say I don't have any magic cast on me and no magic items. Even if I have plenty of spell slotsspell slots, I wouldn't radiate magic, right? What if I'm a warlock with clearly supernatural invocations (say, devil's sight)? What about familiars, do they radiate magic? I think they're BROUGHT by conjuration magic by an instantaneous efect, so they wouldn't radiate magic as they are...
No, I don't think anything you've listed here would show up.

Find Familiar is an instantaneous spell, so once the familiar is summoned, the magic has ended. I don't think most invocations would show up, either, otherwise many creatures with magical abilities would also show up on Detect Magic. Some invocations might show up, but only when active, and only if the effect is clearly described as magical. Any of the invocations that cast spells would of course show up while the spell is active. The only other one I can think of off the top of my head is One with Shadows, but that wouldn't actually show up because you would be invisible (also, I don't remember if it's described as magical).

[Keravath]

Detect magic reads:

"For the duration, you sense the presence of magic within 30 feet of you. If you sense magic in this way, you can use your action to see a faint aura around any visible creature or object in the area that bears magic, and you learn its school of magic, if any."

:vaarsuvius: 1) If I detect disguise self, the caster of detect magic is seeing the illusion covering me, not me. So she wouldn't detect any magic, is that correct? (I don't think the illusion counts as an object)

:vaarsuvius: 2) By the same logic, if I cast mirror image and the opponent has detect magic active, she wouldn't detect magic in any of my images... BUT if I'm wearing, say, a magic armor, she would detect its magic, so the illusions would be useless; is that correct.

:vaarsuvius: 3) Let's say I don't have any magic cast on me and no magic items. Even if I have plenty of spell slotsspell slots, I wouldn't radiate magic, right? What if I'm a warlock with clearly supernatural invocations (say, devil's sight)? What about familiars, do they radiate magic? I think they're BROUGHT by conjuration magic by an instantaneous efect, so they wouldn't radiate magic as they are...

Any comments would be much appreciated.

1) Detect magic is a lot more limited in this edition than in past editions.

RAW, all detect magic tells you is whether there is something magical within 30' of you. You know nothing about it unless you take an action to try and see the magic that you have detected.

"you can use your action to see a faint aura around any visible creature or object in the area that bears magic"

This is a bit ambiguous.

If a creature has a magic item in its pocket or its backpack you can't see it. However, is that creature considered to be "bearing" magic. Bearing can me carrying though I think it is intended in this context to mean "affected by".

Assuming that bearing means affected by, this means that if you use your action, you can see any visible magic items and their aura and you can also see any creatures that are affected by magic but the description doesn't help with magical spell effects.

In your examples -

A) A creature affected by disguise self - this is an illusion spell with range of self. The caster would see you, see that you entirely magical and that the magic type is illusion. The creature using detect magic might guess that you are under the effects of a disguise self or similar spell.

B) Mirror Image is also an illusion spell with a range of self. A caster of detect magic would see that you are surrounded by an aura of illusion magic.

Anything more is a DM call because of the way mirror image is written.

"Three illusory duplicates of yourself appear in your space."

How realistic are these illusions? Are they just visual? Do they make sounds? Do they have odours? The spell states that they move around in such a way that it is impossible to tell which of the illusory duplicates is real.

Do these duplicates also reproduce any magical auras that you currently generate? The spell doesn't say - but a DM could rule either way. Detect magic could be considered a special visual sense that allows you to see the auras of magic that are visible to you. Mirror Image could have been designed to include the magical aura of yourself and anything you carry. A bit far fetched but all the spell states is that duplicates are created and they are impossible to tell apart.

"A creature is unaffected by this spell if it can't see, if it relies on senses other than sight, such as blindsight, or if it can perceive illusions as false, as with truesight."

Does detect magic count as another sense? RAW no - the spell doesn't say anything about that but it would be up to the DM.

Finally, even if a DM ruled that detect magic allows the caster to see which of the creatures was real among the mirror images, they would be the only character who could see it and since it uses their action there is very little they could do about it unless they have a bonus action that they could possibly use. Since anyone else in the fight sees all the images and they are all moving around, I don't think it would be possible for the creature with detect magic to identify the real one to others. (Again a ruling that might vary depending on DM).


C) The sage advice compendium gets into this a bit in terms of identifying what is considered magical and what is not and the ability to do certain things isn't magical even if the execution of them might or might not be considered magical. Spell slots certainly aren't magical - they are the potential to do magic.

"But our game makes a distinction between two types of magic:
• the background magic that is part of the D&D multiverse’s physics and the physiology of many D&D creatures
• the concentrated magical energy that is contained in a magic item or channeled to create a spell or other focused magical effect
In D&D, the first type of magic is part of nature."

This is in the context of using dispel magic and it goes on to add some ways to figure out if something is magical. One of these is if the word magical appears in its description. Invocations are described as "fragments of forbidden knowledge that imbue you with an abiding magical ability." .. which would mean that they might be considered magical and thus could be detected and possibly dispelled.

Personally, I would never rule that way. Invocations, in my opinion, fall into the category of background magic and would not be revealed by a detect magic or be affected by dispel magic - however, some DMs may rule otherwise.

So, in general, I think most DMs would not allow detect magic to work on inate abilities of the character that do not involve casting a spell. Personally, I would limit detect magic to spell effects and magical items.

Finally, there is the question about illusions. For example, a character who casts major illusion creates an entire scene including creatures and objects but none of which are real. Personally, I would allow detect magic to show the caster that the entire area was affected by illusion magic in this case but again other DMs might rule otherwise.

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TL;DR Illusions of any kind are very DM dependent :) ... consult your DM if you want to know how they would rule :)

[Greywander]

which would mean that they might be considered magical and thus could be detected and possibly dispelled.
IIRC, Dispel Magic can only remove spells. Magical effects that aren't spells aren't affected by Dispel Magic. Which is, admittedly, a bit weird, but it at least prevents things like dispelling a warlock's Devil's Sight.