Question: Context
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An evil wizard has used [*True Polymorph*](https://www.dndbeyond.com/spells/true-polymorph) to make one of their minions resemble the king. As a precaution against diviners, the wizard also casts [*Nystul/Arcanist's Magic Aura*](https://www.dndbeyond.com/spells/arcanists-magic-aura), "Mask", for 30 days, which will have the following effect until dispelled:

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> 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.
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The evil wizard then kills the true king and installs their polymorphed pawn on the thrown.

Later, a group of adventurers are trying to find the king at a masquerade party. They know the king is in attendance, but cannot find him due to the festive masks, so they cast [*Locate Creature*](https://www.dndbeyond.com/spells/locate-creature), naming the king as the spell's target. The description for this spell states the following:

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> If the creature you described or named is in a different form, such as being under the effects of a *polymorph* spell, this spell doesn't locate the creature.
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Question
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Does the *Locate Creature* spell fail, potentially revealing to the adventurers that the imposter attending the party is not truly the king? Or does *Nystal's Magic Aura* cause *Locate Creature* to function normally?

Answer: 
Yes, but the spell fails for another reason
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*Nystal's Magic Aura* (MASK) states:

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> 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.
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The Mask is only changing the detected type or alignment of a creature. However, this isn't what *Locate Creature* is looking for:

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> The spell can locate a specific creature known to you, or the nearest creature of a specific kind (such as a human or a unicorn), so long as you have seen such a creature up close--within 30 feet--at least once. If the creature you described or named is in a different form, such as being under the effects of a polymorph spell, this spell doesn't locate the creature.
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As long as you *know* the True King, you can try and locate him. However, if you have not seen the True King, then he would not be a valid target for this as you don't actually know that there is a True King vs the False King.

For the sake of this question, let's say that the party *did* see the True King up close at one point and they attempt to *Locate* him at this party. If so, then *Nystal's Magic Aura* will do nothing to prevent the spell from working because it's only affecting knowing the False King's Type (humanoid?) or alignment via the Mask feature. In this case, the *Locate Creature* would not provide a direction unless the True King is within 1000' of the party.
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> Does the Locate Creature spell fail, potentially revealing to the adventurers that the imposter attending the party is not truly the king? 
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Yes

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> Or does Nystal's Magic Aura cause Locate Creature to function normally?
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No

There is no conflict here - each spell does exactly what it says it does. The target of the *Locate Object* is the (dead) king. The imposter is not being targeted so *Nystul's Magic Aura* has no work to do.

Oh well - "the best laid schemes o' mice an' men Gang aft a-gley"