How can an NPC disguise themselves from the party for an extended period?

Question

I have an upcoming storyline where I would like an NPC to hide their identity to gain the trust of the party. The nature of the ruse will involve them traveling with the party for an extended period (days or weeks) so I need something with a long duration.

This disguise will involve changing the race of the NPC. Effects similar to alter self would be ideal but anything I can find lacks the required duration for my purpose. The Hat of Disguise, Greater modified to be continuous (double the cost) is the best solution I have found but is very expensive at 24,000gp and not something I want the party to potentially have access to.

Currently the PCs are 6th level and will be 7th or 8th when this storyline occurs. The party have a wizard that casts detect magic on everything he sees, a paladin that uses detect evil on every important NPC, and a druid with extremely high perception, I need to be able to fool all of them. They also have a bard and a barbarian but they are easier to trick.

Magic aura and undetectable alignment will get me some of the way there but suggestions that don't involve so many resources are appreciated.

How can an NPC hide their identity from the PCs for an extended period of time?

• Preference is for spells, magic items or special abilities that are available to a broad range of races and classes, but good abilities with some restrictions are also helpful.
• Anything that requires more than two class levels in a non-arcane caster class is less useful.
• I'm looking for low cost, high effectiveness solutions.
• Content from official Pathfinder sources is preferred. Though D&D 3.5 and 3rd party are acceptable if there is no equivalent in pathfinder.

Answer 1

The Perception skill check result needed to penetrate a mundane disguise can be increased to an arbitrary number with a sufficient number of assistants. Each untrained dude that aids another on the NPC's Disguise skill check has a 50% chance of increasing the NPC's Disguise skill check result by 2, and the NPC pays only 1 sp to get a day's work out of an unskilled hireling. (For example, 100 gp puts to work for 1 day one thousand untrained hirelings on the NPC's behalf and yields somewhere around a +500 bonus on the NPC's Disguise skill check.) The downside? Unless the NPC disposes of the hirelings afterward, they're in on the ruse. However, if the NPC dons the disguise far away from the point at which he's introduced, this shouldn't be an issue.

(Note that the GM determines how many folks can aid another on a particular skill check, so, really, a thousand assistants may be too many. If the campaign's already established that only, like, three assistants can aid another with a Disguise skill checks or something, there's this fine answer that'll let the NPC crank his Disguise skill check through the roof.)

A ring of mind shielding is 8,000 gp and stops lie detection and alignment detection magic. The ring has an abjuration aura so, until it's formally identified, it can be passed off as a ring of protection, and typical heroic PCs won't find it very useful if it's looted. If the NPC's other magic items need different aura, as the question mentions, the magic aura spell is probably the best route. Then it's just a matter of the NPC using the Bluff skill a lot.

Consider alternatives to this plot

In my experience, players are a paranoid and innovative lot. An NPC who wants to join the party for any length of time will arouse suspicion. The GM must assume that the players have consumed every narrative wherein someone new wants to join one or more protagonists in their quest only to have that someone new turn out to be an antagonist. Thus the players will resist this NPC joining their PCs.

Then, if the NPC insists, the GM must assume that the players have consumed every narrative wherein someone new is subjected to an interview or interrogation and that the players will use every trick to trip up the NPC. The PCs will likely subject the NPC to background checks and interviews worthy of a job at the Pentagon.

Then, assuming the NPC's façade hasn't cracked and the NPC joins the party, ultimately one of two things will happen.

• The PCs discern the NPC's ruse early. The PCs kill the NPC and take his stuff.
• The PCs don't discern the NPC's ruse. Because the players feel like their PCs did all they could to prevent this outcome, the players feel like the GM cheated, that the betrayal was inevitable, that their agency has been violated, and that the GM should go write a novel.

In other words, either way, the GM's plot occurs, but—also either way—no one's particularly happy about it. I offer below two alternatives to this plot, both of which I have used instead of having the NPC himself join the party.

• Have the NPC employ minions. Instead of endangering himself personally, have the NPC spend some cash or persuade some dupes to keep a distant yet careful eye on the PCs and report back. Or have the NPC hire a spy outright to infiltrate the PCs' ranks instead of the NPC doing it himself. (Note that the NPC can use a sending spell to communicate with his spy—it's very nearly undetectable on the target!)
• Have the NPC employ magical surveillance. A scrying spell on the PCs—or their mounts!—can often provide as much information as actually traveling with them. The spell greater scrying in particular has a duration measured in hours. Then, when the PCs have almost reached their goal, the NPC can teleport to the PCs' location and interfere.

Both methods are low-risk, high-reward strategies that don't see the NPC endangering himself directly. In fact, they're methods that reward the PCs' paranoia without spoiling the DM's plot. Further, in the case of minions, NPCs are introduced that, if not slain, can be used in later adventures.

Answer 2

Through the use of the disguise skill.

Unlike magic, there isn't a limit on how long a mundane disguise can last. However, there are magical disguises that last for a permanent duration and can be combined with the disguise skill. If the NPC is a Kitsune, by sacrificing a single level and a single feat, you can get a +52 bonus to Disguise Skill checks to hide yourself without any ranks in it, this should allow you to fool the druid. Additionally, as their ability is supernatural, detect magic does not detect it as a polymorph spell, if it could even detect it. Here are the components to doing so.

1. Disguise Kit (+2 Circumstance):

This kit contains tools like makeup and fake facial hair, and provides a +2 circumstance bonus on Disguise checks. A disguise kit is exhausted after 10 uses.

2. Change Shape (+10 racial):

Change Shape (Su) A kitsune can assume the appearance of a specific single human form of the same sex. The kitsune always takes this specific form when she uses this ability. A kitsune in human form cannot use her bite attack, but gains a +10 racial bonus on Disguise checks made to appear human. Changing shape is a standard action. This ability otherwise functions as alter self, except that the kitsune does not adjust her ability scores and can remain in this form indefinitely.

3. Magic Rules for Polymorph Subschool (+10 untyped):

First we look at change shape again

This ability otherwise functions as alter self, except that the kitsune does not adjust her ability scores and can remain in this form indefinitely.

Alter Self is a Polmorph subschool spell, the polymorph subschool says:

Polymorph: a polymorph spell transforms your physical body to take on the shape of another creature. While these spells make you appear to be the creature, granting you a +10 bonus on Disguise skill checks, they do not grant you all of the abilities and powers of the creature. ...

Thus giving a +10 bonus when we use Change Shape.

4. Realistic Likeness (+10 Circumstance):

Benefit: You can precisely mimic the physical features of any individual you have encountered. When you use your racial change shape ability, you can attempt to take the form of an individual, granting you a +10 circumstance bonus on Disguise checks made to fool others with your impersonation.

5. Seamless Shapechanger Vigilante Social Talent (+20 Untyped):

If we look at this Social Talent, it states:

Seemless Shapechanger (Ex): The vigilante seamlessly adopts any persona he assumes with magic. The vigilante adds his seamless guise bonus to the bonus on Disguise checks that he gains to assume the shape of another creature with a polymorph spell or effect. A vigilante must have the shapechanger subtype to select this talent.

Looking at Seamless Guise it states:

A vigilante knows how to behave in a way that appears perfectly proper and normal for his current identity. Should anyone suspect him of being anything other than what he appears to be while either in his social or vigilante identity, he can attempt a Disguise check with a +20 circumstance bonus to appear as his current identity, and not as his other identity.

Which means we get a +20 circumstance bonus when using our Change Shape ability.