Y'know, it occurs to me - Movie!Sonic has a lot more in common Shadow than any other version of Sonic that I know of, and that creates a unique storytelling opportunity that wouldn't have been possible before.
Because originally, Shadow having a dark and traumatic backstory was what separated him from Sonic. Their similarities came out more in their confidence, their playful attitude, and even their withdrawn demeanor (though Shadow's is more extreme). Sonic's genuine ability to be carefree and optimistic was his biggest difference from Shadow.
In the movies, Sonic is... not nearly as put-together. Just like Shadow, his personality is shaped almost entirely from the result of tragedy. Both of them had to watch their closest family member get shot trying to save them from raiders (who were specifically targeting them for their powers) by sending them to Earth. The difference here is that, for Shadow, this event is fresh in his mind, while Sonic's had ten years (give or take) to accept what happened and move on.
Except, there's more, because losing Longclaw is itself not the main thing informing Sonic's character - it's the fact that he spent those next ten years in near-total isolation. Also similarly to Shadow, he took the last words his family said to him very seriously, and she told him to stay hidden no matter what. Combine that with the natural fear of what being found did to Longclaw, and the majority of Sonic's life has been spent hidden away, looking out at the world but unable to participate in it.
Remind you of anyone?
(I swear if the movie doesn't make a point about this parallel specifically I'm gonna lose it)
Normally, Sonic is a silly and upbeat character because that's just how he is by nature, and the feelings he keeps to himself are rarely detrimental to his health. In the movie universe, Sonic is silly and upbeat because he needed to be that way in order for his life to be bearable.
His constant chatter isn't quirky for the sake of it, it's a habit he developed out of necessity because there was no one else to talk to. He compulsively needs to fill the silence because not doing that would only reinforce how alone he was, and it's something he can't shake off even when he's not by himself anymore. His primary method of handling his feelings is to ignore them until they literally explode out of him with lightning firing everywhere.
All of this to say, a Shadow meant to be a foil to this Sonic is going to look very different from the Shadow we're used to. From what little about the movie's events have been described as of writing this, I'm inferring that Shadow's actually going to be a lot more open about his motivations for revenge than he was in the game, and that puts Sonic in the very interesting position of being more closed-off than Shadow.
Because sure, he might try to connect with Shadow's pain like he did with Knuckles. But because Sonic and Knuckles's history was so directly connected, they didn't really have to... talk that much about it. Sonic could acknowledge that they both lost their families a long time ago without having to go into detail about it or the aftermath. And because it had been so long since it happened, it was a lot easier for them to put it behind them and move on.
Shadow can't do that, because for him, Maria was lost very recently. He's not going to accept "you can move on and find new people to care about" as an option, and Sonic can't very well tell him to just ignore it like he did, either. Shadow isn't going to do the whole repression shtick.
For the first time, getting through to Shadow may just depend on Sonic being able to acknowledge his own pain, first. After all, how's Shadow supposed to interpret Sonic, if not as some random guy with a perfectly happy family and an obnoxiously happy attitude telling him that he needs to just, get over what happened to him? How can that come across as anything but naive and shallow without understanding how much Sonic suffered to get to this point?
(It's still a little naive and shallow even with that in mind, but the reason for that isn't because he has no perspective on what experiencing a violent tragedy is like - it's because his only known way of handling it is to leave it in the past and Not Think About It)
Though I do wonder if there's room for Sonic to initially clam up on his emotions even more after meeting Shadow for a bit? Like, he learns to some extent what happened, and is like "aw jeez if this is what could happen if I let myself be more upset about my lot in life then I REALLY need to reign it in" which is the exact opposite lesson he needs to learn but would be really interesting to watch
Point being, I think Sonic and Shadow are being set up as even more like mirrors to each other than usual, and I can't wait to see what they do with that potential
Hopefully. But I doubt.
