I TOLD YOU ALL IT WORKED LIKE THIS!! IT DOES EFFECTIVELY CHANGE THE CREATURE TYPE!! 5.5E FOR THE WIN! CHANGING CREATURE TYPES WITH THIS IS RAI!!

So my Hold Person spell will work on a Beholder? Neat....

willing creature

Technically you could enchant a creature into being willing then changing it into a humanoid and possess it with magic jar.

So, for a 2nd level spell, meant to *mask*  a creature type, you're turning a creature into another creature type, allowing Hold Person to work on Dragons/Beholders/Owlbears/Mimics/Animals/Golems/Celestials/Fiends, turn a Dragon into a Fiend for Smiting purposes, and turn anything into a specified creature type for Antipathy, Hallow, Glyph of Warding, Guards and Wards, Forbidance, or any other spell that works on specified creature types?

And this is an illusion spell of 2nd level.

/design/fail.

If someone were to cast this on a magical item to make it appear non-magical, would Detect Magic still sense the illusory magic from Nystul's Magic Aura around the item?

Quote from Dan_Solo42 >>

So, for a 2nd level spell, meant to *mask*  a creature type, you're turning a creature into another creature type, allowing Hold Person to work on Dragons/Beholders/Owlbears/Mimics/Animals/Golems/Celestials/Fiends, turn a Dragon into a Fiend for Smiting purposes, and turn anything into a specified creature type for Antipathy, Hallow, Glyph of Warding, Guards and Wards, Forbidance, or any other spell that works on specified creature types?

And this is an illusion spell of 2nd level.

/design/fail.

 That is a real possibility, but the creature this is cast on needs to be a willing creature. Though, I'm sure there are ways to coerce them to be willing, such as Suggestion.

When you cast this on a non-humanoid creature and choose humanoid for the creature type, will you be able to cast Animate Dead on the corpse because it’s considered humanoid to spells and magical effect?

Right. And using a charm spell to make them willing, magic aura to make them able, then a hold person spell to make it work on a beholder (or powerful monster of choice)- well… that’s a fair trade vs a single level 4 (or whatever level) hold monster. 

Willing Target!!

That seems like more steps than it's worth, I think the real power of this spell is in changing yourself to a creature type that can't be effected by a lot of spells.  In a good DMs hands this spell can get crazy, they could have the evil wizard make fake magic items to chase, while you're busy with that they can be turning the undead army they have into celestials so your cleric can't turn them. 

Technically technically: An enchanted creature isn't willing. Their will stays the same, its only being overridden by your will. If it's not their will, they're not willing.

Suggestion might actually work, but that still requires the target to think that your suggestion is rational (rules-lawyers: yeah, I know about the change -- but the DM gets the final say, and very few DMs would rule it that way). Personally, I'd rule that Charmed creatures' wills are overridden; and so exploiting that to apply magical effects equals an automatic failure. Buuut, if you successfully influence a charmed creature and then unenchant them, you're good to follow through if they're still on board with your idea. 

they really should have clarified the wording with this spell a lot.

Clearly the intent here is to have the creature act as the other creature type for the purposes of detect evil and good, spells with triggers like sequester, alarm and glyph of warding, and possibly even hallow, with it not being supposed to change the creature type for the purpose of being a legal target of stuff like polymorph, magic jar, hold person etc. 

Perhaps the designers simply hoped that the room for abuse would be minimal when the spell can only target willing? Who even knows

This is the correct answer IMO.

Nystul's Magic Aura is a spell from the Illusion school. It is masking your creature type with a glamour, not physically changing your creature type. Nystul's could definitely make it so spells or abilities to detect undead will not work on the vampire mage NPC who has this cast on himself because the illusion fools the detection magic. But, Illusion spells do not fundamentally alter you in any way. Because of this, you cannot use Nystul's to somehow trick the Magic Jar spell into working on a creature that isn't a Humanoid just because you placed an illusion on them.

Now, if Nystul's was a spell from the Transmutation school then I'd be more inclined to agree that it could allow shenanigans like this. In that case, it would physically alter your body like how Alter Self physically changes you. But, Nystul's is not a Transmutation spell and because of that a DM could correctly say "No, you cannot use this spell to cast Hold Person on the dragon. Nice idea though!"

With that said, this spell is narratively very useful for the DM to foil detection abilities and spells the party may employ or it could be very useful for the party to cast onto the Rogue before they try to sneak into an undead filled dungeon to scout around.

The following are the ONLY valid interpretation of this spell unless you are running some kind of Homebrew rules which change the system.

With this spell:

You CAN make a WILLING Humanoid seem to be Construct, and thus protect them from Charm Person.
You CANNOT make an UNWILLING Fey be a Humanoid, thereby making them susceptible to Charm Person.

I disagree wholeheartedly with any other interpretation. 100% this was the intention, and 100% that is what it says it does. 100%. Inarguably. It's not even really arguable given the crystal clear verbiage and the rules elsewhere on Spellcasting, Interpreting the Rules, and Schools of Magic.

I'm gonna climb up on my soap box here, but this is for the hundreds of veteran DM's that I see making the same mistake over and over and over. 

The Rules as Written are crystal clear here. This spell clearly and SPECIFICALLY states "spells and other magical effects treat the target as if it were a creature of the chosen type." There is ZERO rule of greater specificity anywhere in the rules that overrides this. Most crucially, the GENERAL descriptive rule on what the School of Illusion is does not override this. In fact, it doesn't even come into play in this context since the spell is crystal clear.

The definitions of the Schools of Magic aren't specific when it comes to interpreting the rules of a specific spell. They're general. The SPECIFICS of a given Illusion spell OVERRIDES the GENERIC definition of what Illusion means.

Every. Time.

You CONSULT the GENERAL only when there is no SPECIFIC that applies. That is how ALL rules work in 5E: not just the rules on spellcasting. If you disagree, you may want to re-read the rules on how to interpret the rules.

I have found that far too many seasoned DM's of earlier editions skip that section, and they're bad 5E DM's as a result. It is a constant source of friction among new players, who rightfully call the DM's out for being bad DM's. 'Cause they are when it comes to 5E. RTM.

I see this argument made all the time when it comes to Spellcasting and Schools of Magic, and it comes from DMs / players that either love complexity, or have been tainted from the complexities of previous editions, and haven't truly embraced the 5E way (or, as noted above, skimmed or skipped the sections on How to Use the Rules).

There are literally no rules that establish that the School of Magic overrides the VERBIAGE of a SPECIFIC spell of that school. In fact, LITERALLY the opposite is true! And Thankfully! Trying to interpret such a system that works in the proposed fashion would be a NIGHTMARE!!! Chaos!

That's not how the rules of 5E work. Specific overrides general. You consult General when there is no relevant Specific. The general rules of how Illusion magic works or Transmutation work are the FALLBACK, not the OVERRIDE. The definitions of the Schools of Magic are the GENERAL rule that provide context of WHAT DO I DO when something comes at at my table, but there is no part of that SPECIFIC spell that guides you to a valid interpretation. It's not Rocket Surgery! The SPECIFIC verbiage of a given spell OVERRIDES that GENERAL type of spell that it is! It's just how it is. The School rule should ONLY be consulted when it's not clear from the spells verbiage how to proceed.

That is 100% NOT the case here!!! The spell is clear. ALL spells and ALL magical effects consider the Creature Type changed Period. End o Story. You Lose! Good Day Sir! :-)

You can't just say "Well, illusion really shouldn't be able to do this...". That not how this works. That's not how any of this works. If a situation arises at your table where the verbiage of the SPECIFIC spell falls short, then yes, by all means, FALLBACK to your understanding of the School, its Spell Level, the Spell Level it is cast at, or ANYTHING ELSE you want to try to make a ruling. But, THOSE THINGS DO NOT OVERRIDE CLEAR WORDS THAT CLEARY APPLY!!!!! Unless those words are overridden elsewhere, they TRUMP those other things!!!

Now, if you don't like the CRYSTAL CLEAR SEMANTICS of the spell, fine, change it. That's fine, and you're 100% within your rights to do so for your table. But, you shouldn't try to change the behavior and justify it by breaking the entire mechanics of the how rules are meant to be applied in the game of 5E. Just change the specific spell. Or remove it from your game if you don't like it. Those are Good Faith solutions. Saying General overrides Specific is not Good Faith. Saying this spell isn't specific and crystal clear is not Good Faith. Those are not Good Faith interpretations. Those are Bad Faith, and would leave a Bad Taste in any knowledgeable players mouth. 

Just my 2 cp.

Yep normally the school of magic has no real impact beyond specific features that use them. Example: truesight seeing through any illusion. Wizards of a specific spell school type having features focused on that type. Etc. Anything regarding the school type affecting a spell is homebrew unless specifics are present as prior. This is a 2nd level spell but some considerations are its a willing target and a touch spell. You have to move in and have someone be willing to have any impact from this spell (most wizards aren't going to get a whole lot of use from this at the level they get it, and by the time some nutty combos come in play game balance is way outta wack in favor of casters as is without needing this spell).

Couldn't agree more, rules are crystal clear on how this spell works. However, that is exactly why I'm banning the spell at my table because RAW the spell is not remotely balanced for my table which is what I think people are ACTUALLY upset about. Obviously you were more focused on clarifying how the spell works but let me ask you if you think the spell's actually balanced which I think is an equally important question?  

Awesome! So my fairy can use a 2nd level spell scroll to make herself humanoid for 24 hours, then make a simulacrum. I know what I'm doing after my long rest.

Can a sentient object deny nystul's magic aura like an unwilling character?