"...What would they turn into?"
Basically, imagine that the various human characters have been turned into Pokémon either by magic or by ending up in the Mystery Dungeon world.
Did you imagine it? Good. Now write down into which species they have been turned and why do you think so. I'll start with some suggestions of mine, related to the three main human characters.
∙ Ash -> Riolu
This is mainly related to his strong connection with aura, as well as his role in both the Lucario movie, the Pokémon Ranger special about Aura Sphere Riolu and the legend about the Aura Guardian who defeated Spiritomb with the help of a Pikachu. Also, the Riolu line is known for its incredible athletic feats, and Ash has shown some athletic talents in some circumstances. Besides, they both wear blue, so they are pretty good together.
∙ Jessie -> Female Pyroar
Between the iconic hairstyle, the elegance of the two, their fiery personality, their mutual connections with an evil organization (Jessie with Team Rocket and Pyroar with Team Flare), and the attitude of a leader, I find this match absolutely perfect. I mean, Jessie even used "Flamethrower" once, so there's the proof.
∙ James -> Mareanie
I blame SM for that, but wow! They look sooo much alike, to the point that I wonder if Game Freak took inspiration from James to draw Mareanie. Aside of their "hair" color, I would find it ironic that James turns into an unhuggable critter, especially considering that he is quite prone to painful "hugs".
Another match which I think could somewhat work is with Alolan Meowth. This could be a nod to Meowth himself and to the fact that Alolan Meowth were raised in wealth, which basically mirror somewhat James's past. Also, they both collect shiny objects, with James collecting bottle cups (bring them back, anime!) and Meowth collecting coins.
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