I have to wonder how Stan feels about seeing Dipper hanging out with his brother’s pokemon. Or Gideon, for that matter. Like I would imagine that Ford’s pokemon would at least have some idea who Stan is, even if that is “the guy who pushed our trainer into the portal” or “some guy who moved into our trainer’s house.” Admittedly, I’m not super well versed on Pokémon but I feel like that would be something right?
Dipper found slowpoke at the same time as Journal 3. He hides him from stan in the same vein as how he hides the journal. But slowpoke and Stan should recognize each other as Ford and Stan actually caught him together when they were kids... He wouldnt have seen stan at the time of the portal incident though cause a lot of them were in their pokeballs at the time. I imagine after Stan gets his hands on Journal 3, he would end up hanging out with slowpoke a lot.
The only people that knew Gideon had a Spiritomb were Dipper and Mabel, cause it's supposed to be the equivalent of that cursed pendant in Hand that Rocks the Mabel. Spiritomb's thing is that it's literally just a rock that has 108 ghosts inside of it.
In my mind Ford put Spiritomb with journal 2 to watch over it, so it wouldnt have seen what happened to him. But it didnt really like Ford very much, so it wouldnt care one way or the other about Stan anyway. It's supposed to be a mischievous pokemon, so I think it just likes causing trouble in general.