How does the Ring of Mind Shielding interact with effects that affect a certain alignment?

Question

The Ring of Mind Shielding, an uncommon magic item (DMG, p. 191), has the following property (emphasis mine):

While wearing this ring, you are immune to magic that allows other creatures to read your thoughts, determine whether you are lying, know your alignment, or know your creature type.

How does this interact with effects that affect creatures of a certain alignment? After all, by common sense, something can't affect you based on your alignment if it doesn't know it.

Most notably, the Outer Planes affect "dis-aligned" creatures, as specified in the DMG. There are also some magic items that correspond to certain alignments, such as a Candle of Invocation or a Talisman of Pure Good / Ultimate Evil.
Spells such as Glyph of Warding can also affect creatures of certain alignments.

The same question rises for the matter of creature types, but I suspect the answer will be the same.

Answer 1

They affect you as normal

you are immune to magic that allows other creatures to ... know your alignment

None of the effects you mention do that, so the ring has no effect on them.

Answer 2

If a glyph of warding falls in a forest and nobody is around to see it, does it actually reveal alignment?

Glibness aside, let's take as a given that a glyph of warding could be given an effect which reveals the alignment of a creature who enters it. The nature of how it does this is irrelevant. When a creature wearing a ring of mind shielding enters the warded space, what happens?

Option One: The Quantum Glyph

If the creature wearing the ring is the only creature capable of perceiving the effect in the room, the effect will be generated as usual. If there is any way for the effect to be perceived, the effect will be obfuscated in some way.

This is operating under the assumption that, per the item's description, any magic "that allows other creatures to...know your alignment" does not function, and that this rule can be interpreted to mean that no matter how convoluted of a magical Rube Goldberg machine you create, the ring's wearer cannot have their alignment revealed.

Option Two: No Inherited Traits

Alternatively, we could rule that spells which are cast directly on the creature wearing the ring don't work, but those which are present simply in the area do.

In this case, we are ruling that the spell will take effect because the spell is not a creature sensing your alignment; it is simply something that happens as a law of the universe. It isn't choosing to reveal your alignment any more than a scale would reveal your weight. It's not a creature taking action on information; it is a piece of scenery that is reacting as it naturally would to your presence.

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Personally, I can see a reasonable argument to be made for either option, depending on how we understand the plain text in the item's description-- which means that we're back to the ol' "rulings, not rules" chestnut. Were this particular case to come to me as a DM to adjudicate, I would turn to the classic Rule of Cool.

A player who gets this ring (and uses a precious attunement slot for it!) will likely feel much cooler if we make it so that they are truly immune to having their alignment discerned, as I have found that players are generally happiest when their magical items do, in fact, work. Taking away part of the function of a magic item because I, as the DM, have found a clever workaround is what I believe the kids these days call "a dick move".

However, were the players to be up against an enemy with the ring, I would allow a suitably clever solution (such as a well-placed glyph of warding) to succeed, because I've found that rewarding players for being clever within the bounds of the rules is the best way to avoid other rules-lawyering or shenanigans.

In short: There's compelling arguments both for and against allowing the ring's ability to be subverted, and as with many things in D&D, the correct ruling is whichever one will make for a better narrative and more enjoyable game given the context in which the question arises.

Answer 3

No for the items and spells and yes for the planes

The Ring of Mind Shielding description states:

While wearing this ring, you are immune to magic that allows other creatures to read your thoughts, determine whether you are lying, know your alignment, or know your creature type.

The items you have mentioned works through magic. The Volo's Guide to All Things Magical says (p. 14):

The process of making a complex magical item begins with an initial plan for what the item will do and preparation of the necessary focal stones: gems that hold the spell powers of the item until its component magics are combined into a coherent, controllable whole. (The types of gems that are used in magical item construction, including those that make the best focal stones, are detailed a later section of this chapter.) The necessary spells to create the effects the future item will release are gathered or researched. Note that what spells can be best adapted may be a matter of some speculation and is not necessarily clear-cut and definite at this point - and mistakes made at the outset can doom an otherwise well-conceived item.

But the dis-aligned damage from the planes is related to the essence of the plane and creature itself. The DMG says (p. 58):

A plane's alignment is its essence, and a character that doesn't match the plane's alignment experiences a sense of dissonance there. When a good creature visits Elysium, for example, it feels in tune with the plane, but an evil creature feels out of tune and more than a little uncomfortable.

The plane doesn't need to know your alignment: you'll be uncomfortable because the plane is very different from you. Imagine a good character in an evil plane, seeing all that cruelty; doesn't matter if he/she is using the ring or not, he/she will be uncomfortable with that and suffer the psychic dissonance effect (if you choose to use this rule), period.

Answer 4

They function as normal. The Ring of Mind Shielding blocks magic that lets other creatures know your alignment. In the Glyph of Warding example, for instance, the glyph functions as normal since the glyph isn't a creature. The Outer Planes' Psychic Dissonance affect works as normal because the Outer Planes aren't a creature. The magic items also aren't creatures, so they still work.

Answer 5

Direct vs Indirect

There is a large amount of disagreement on this question, based on how the wording is interpreted.

For this answer, I'm splitting the arguments into two camps: direct and indirect.

Direct

This argument is that the ring only affects magic that directly targets the wearer. Those siding with the direct argument are the (current) majority, based on a number of replies and upvotes to those replies.

Indirect

This argument is that the ring affects all possible means by which the wearer's alignment could be revealed, even if the magic is only indirectly informing other creatures of the wearer's alignment. There appears to be a minority of such people, but they are firmly disagreeing with the arguments that the ring only affects creatures that directly use magic against the wearer.

Understanding the word "allow"

The disagreement on this question appears to come from different people using different definitions of the word "allow". So, let's break that down by listing potentially applicable definitions of that word.

Allow

1. PERMIT
2. to fail to restrain or prevent
3. to give an opportunity : PERMIT

A word in all caps means it is referencing another word to give context/explain a given meaning. So, we dig into the word "permit".

Permit

1. to consent to expressly or formally
2. to give leave : AUTHORIZE
3. to make possible

And finally, authorize.

Authorize

1. to endorse, empower, justify, or permit by or as if by some recognized or proper authority (such as custom, evidence, personal right, or regulating power)
2. to invest especially with legal authority : EMPOWER

(I excluded some definitions because they weren't applicable to the situation, in my opinion. I could give a breakdown of why for each, but the pedanticness of this answer is already more than this community generally tolerates.)

Nine interpretations

1. you are immune to magic that permits other creatures to know your alignment
2. you are immune to magic that fails to restrain or prevent other creatures to know your alignment
3. you are immune to magic that gives an opportunity [for] other creatures to know your alignment
4. you are immune to magic that expressly consents [for] other creatures to know your alignment
5. you are immune to magic that gives leave [for] other creatures to know your alignment
6. you are immune to magic that authorizes other creatures to know your alignment
7. you are immune to magic that makes it possible [for] other creatures to know your alignment
8. you are immune to magic that endorses, empowers, justifies, or permits via the proper authority other creatures to know your alignment
9. you are immune to magic that invests other creatures with the legal authority to know your alignment

(The authority of the last two refers, in this context, to the laws or god or goddess of magic's authority.)

So, there are up to 9 ways to interpret the wording of the rule. I make it a point to list all potentially relevant interpretations, as the disagreement on this question largely boils down to interpretation of what a word means.

That's a bit unwieldy to handle, and largely unnecessary, so let's see what we can reduce.

Thinning the results

We'll address definition 3 first, as it is invalid to use that definition in this context.

That particular definition of "allow" is an "intransitive" definition, meaning that there is no direct object.

Direct Object

In English grammar, a direct object is a word or phrase that receives the action of the verb.

In this case, it is "creatures" that are receiving the action of the word "allow". Therefore, we cannot use definition 3, as that is the intransitive usage (see more on the dictionary's page, including examples of that definition to see why it doesn't apply.)

We can then throw out 1 and 6 as well, as "permit" and "authorize" are covered by their own definitions, so those can be handled by 4 and 7, and 8 and 9, respectively. Likewise 5 is covered by "authorize"'s definitions.

Numbers 8 and 9 are similar enough that we'll just use 9. Likewise, for something to consent it has to have the authority to give consent, so we can roll 4 into number 9 as well.

Finally, I reject definition 2 from applying to this situation, as that is the "How could you allow this to happen!?" definition. For that to be what was intended, it would mean that the default state of the universe was that creatures could the alignments of others, and that this ring prevented magic that did nothing to stop that. That doesn't make much sense to me.

Two unique interpretations

That leaves us with just two interpretations:

7. you are immune to magic that makes it possible [for] other creatures to know your alignment

9. you are immune to magic that invests other creatures with the legal authority to know your alignment

Interpretation: Make is possible

This is the definition that the indirect camp is using.

The ring makes the wearer immune magic which makes it possible for other creatures to know the wearer's alignment.

Interpretation: Invest with legal authority

This is the definition that the direct camp is using.

The ring makes the wearer immune magic which invests other creatures with the legal (magical) authority to know the wearer's alignment.

Conclusion

This brings me to the unsatisfying conclusion that both interpretations appear valid.

As such, it is up to the DM to decide how they want their campaign world to operate.

On the one hand, it makes sense, based on the name of the ring, that the wearer is shielded from all means of their alignment being detected.

On the other hand, it could create some very convoluted reasoning to describe how or why a hypothetical magic item doesn't react as it normally does, just to prevent the wearer's alignment from being able to be deduced.

Ultimately it is up for each DM to decide what works best for their table.

_{For those who are disappointed in this answer not resulting in a clear answer, you are not alone. I started it thinking it was going to lead me in a specific direction, but ultimately the definition of the word "allow" does appear to be ambiguous enough that either interpretation is valid. I don't want the effort to go to waste though, and I figure providing a basis for each interpretation is valuable to DMs in deciding on their own ruling. Or someone can poke a hole in one of the two interpretations and post their own definitive answer.}

Answer 6

The item is referring to effects such as Heart Sight which say "The sprite also knows the creature's alignment". It doesn't stop other alignment based effects from activating as they do not require the alignment to be known.

Similarly, if a goblin wears this ring that doesn't mean that a ranger with favored enemy (goblin) won't be able to use their bonuses.