Regarding animists (spoiler)

[Takatifu]

How would an Animist with the

Spoiler:

Seer practice percieve themselves and the other PCs while using Apparition Sense?

[Sibelius Eos Owm]

RAW I'm pretty sure that, at least for the majority of the AP, the PCs don't count as anything listed in that ability. Furthermore, that ability is not a precise sense (like sight) but rather only allows the Animist to pinpoint the location of a subject (such as you could with hearing). The strictest reading seems to suggest that there is no obvious interaction between the circumstances about town and this sense.

That said, if you were looking to do something a little extra special, you could easily decide that this ability manifests with some kind of visual (or non-visual) cue for the Animist player. Perhaps some minor quirk or sixth sense that tells them where their allies are at all times without them being able to place why they know, or if they guess, why their allies could be tripping the sensor.

Be aware, however. If you decide that PCs count for the purposes of this sense, then at minimum all the inhabitants of Willowshore do as well, and this very probably includes many, if not most other inhabitants of the surrounding area. There is an argument both for and against the agents of the big bad being included in that list, too.

For Clarity:

Apparition Sense allows you to detect hidden spirits, haunts, and undead within 30'. It doesn't necessarily let you see them, if they are invisible or hidden, but even if it did, the mindscape seems to treat the PCs and all Willowshore inhabitants as living, corporeal creatures--at least if they were before being transported.

The mechanics for immersive mindscapes like Willowshore, as well as the descriptions in the AP suggest that life inside the fog boundary is largely indistinguishable from normal.

[Quentin Coldwater]

(I'm a player, and slowly prepping to GM as well, but I don't have the entire background knowledge, so take with a grain of salt.)

Technically, I believe the players are spirits, but they function as if they're normal living creatures. Everyone and everything in the demiplane/pocket dimension still functions just as they did before the loop started.

Having the animist player immediately feel something's off feels like a big spoiler, but I have no idea how you could subtly hint without giving something away immediately. Maybe because they've been living in this loop for over a hundred years, they've sort of gotten used to it, kind of like how you don't feel the clothing you're wearing It's just become part of them now, even across multiple loops. It's kind of a cop-out answer, but I personally think immediately revealing something's off about the PCs (and everyone else) ruins a bit of the surprise.

[James Jacobs]

Spoilering to be extra sure not to spoil...

Spoiler:

Apparition Sense won't detect the PCs, because they're not spirits, haunts, or undead for the bulk of this campaign—it wouldn't be until they transmigrate into the living world at the end of book 3 that they'd register as undead or spirits. Specifically, in order for Apparition Sense to detect invisible or hidden spirits or undead, the thing needs to have the Spirit or Undead trait, which the PCs don't have. Technically, when they DO transmigrate, they're still living creatures and not undead; they're more like phantoms in this section, but I'd say they'd still show up to Apparition Sense as spirits.

Until then, the PCs are treated as if they were alive, because they ARE alive for most purposes from the context of being inside the mindscape. If a PC somehow managed to get OUT of there and then use Apparition Sense, they'd perhaps be able to sense the spirits and ghosts of the people of Willowshore (including PCs that are still in there)... that's similar to how Mago Kai's exorcists are finding things out, after all.

(If a PC is an ancestry that has the spirit trait or undead trait already, then yes, they'd show up normally to the sense.)