I miiiiight be wrong with this, but don't you guys think it's too coincidental that Marshadow is in a movie supposed to be the 20th anniversary movie? And part of the movie is about reminiscing Ash's past? And yet, these characters appear out of nowhere, alongside Ho-oh, this one rival with a Incineroar? Or a Lucario and a Pochama being these trainers' mons? Ash being completely out on his own besides these characters?
I think Marshadow does more than simply hide in one's shadow.
>Able to conceal itself in shadows, it never appears before humans, so its very existence was the stuff of myth.Could it be that he might actually be able to temper with one's memories in some manner? Or take the shape of someone's shadow? Being able to project itself as various shadows? Don't ask me why he's Fighting type, I dunno.
This is completely unrelated, but check out this video of Doraemon to check out what I mean. Or just skip to a few scenes, I dunno, the video itself is not the focus (it's in fucking hindu to top it off), but how Nobitas' shadow appears in the episode itself.
https://www.youtube.com/watch?v=JmQwDUnnFAwI'm just throwing a bone to see what you guys think, don't want to jump into any wild conclusions.