i will hate Sonic Prime, even from beyond the grave, but if i had to go by a rule where i could change one thing, but keep everything else the same, it would be Sonic's response to the alters.
he switches between recognizing them as their own people and as 'copies', depending on whatever's more convenient for the writers at the time, and it just feels really out of place.
yes, each iteration comes with different characterizations, but i feel there's always particular details that just... shouldn't be changed, no matter how different the setting is from the original, y'know? at least for official, big-name esc stuff.
and one thing that just never made sense to me and continued to feel entirely out of character for Sonic is how he sees his supposed friends as just 'copies' at all.
in the storybook games, Sonic's confused for 5-10 seconds or so before he understands and accepts that those with the same faces of his friends are entirely different people with their own entirely different, separate lives. he can differentiate them from those in his own world.
even if that wasn't the case, the show still made him ridiculously obtuse and be wishy-washy on identity, in terms of writing, and none of it is ever resolved. it's just as if Sonic and Shadow were correct in that they weren't 'real' people.
besides, keeping that about Sonic would've given a lot more room for development on his struggles and slowly declining perception of himself, rather than have it come out of nowhere that he's suicidal for, like, 3 minutes, then just ignore it and leave it at "Nines is just being mean, waaa :(".
i'm an emotional masochist on writing, make my devastated heroes devastating, you cowards.