"mashounen1945" on Tumblr had come up with a couple of theories after pointing out how weird it actually is when Tails gets the Rhythm Badge in Sonic Adventure 1. After finding the original post, I came up with a small idea for a story, but I'm not sure if that story will ever materialize, so I'll just put it out here.
Here's the copy-pasted original post (this is the link, if you wanna look it up for yourself: https://mashounen1945.tumblr.com/post/736100878031929344/something-crazy-i-realized-about-tails-in-sonic):
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"Something crazy I realized about Tails in Sonic Adventure 1" by "mashounen1945"
I’m replaying SA1 right now (on a Dreamcast emulator, because f*** those buggy-as-heck re-releases, am I right?). I’m jumping from one character to another (while always staying on one savefile) to play through every event of the story in order…
And as far as I saw, Tails is the only playable character who gets one of his upgrades during a dream.
He grabs Froggy (and the red Chaos Emerald with it) at the end of Sand Hill, sees Tikal’s hitodama floating around him, the dream/flashback in the Knuckles Clan’s ancient walled city starts… and when he wakes up from that dream, he’s got the Rhythm Badge on his chest out of nowhere and is suddenly able to lethally slice everything around him non-stop with reckless abandon.
Yep, he straight-up dreamed the Rhythm Badge up and materialized it outside of the dream.
Just consider the in-universe implications:
Sonic: “Hey Tails, that’s a cool amulet! Where’d you get it?”
Tails: [with Dr Light’s English voice from Mega Man 8] “That’s a good question.”
I’m also trying to think of some other videogame, TV series, movie or comic that had done something like this, but I can’t come up with anything. I’ve seen a few people suggesting a few examples, though: one power-up in a Castlevania game, Psychonauts, The Legend of Vox Machina, the seagull appearing at the end of The Legend of Zelda: Link’s Awakening (it’s implied the seagull is a real-life incarnation of Marin created by the Wind Fish), the Klonoa series’ entire universe…
Someone else mentioned the possibility of Tikal granting the badge to Tails through the dream. If that’s true, then she’s one hell of a powerful spirit. Basically, “Tikal OP, plz nerf”.
Another possibility I’ve considered is that, perhaps, those flashbacks are not dreams and Tikal’s spirit has the power to literally send the characters back in time so they can witness what happened to the Knuckles Clan and where Chaos comes from. Super-powerful ghost Tikal headcanons aside, it’d also imply Tails retrieved the Rhythm Badge from its place at the Echidnas’ walled city in the past.
Like… He grabbed the badge with his own anthropomorphic fox hands in the past, and then he carried that badge to the present. This would mean that, if either Tails, Sonic or any of the other four playable characters in SA1 hadn’t “followed the script”, they totally could have changed history at any point around the time when the Knuckles Clan was decimated by Chaos.
Anyway, thanks for reading my ramblings, I guess. SA1 certainly has one bizarre, trippy story when you think about it, especially regarding Tails’s story.
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Well, here's my idea for a story:
It's very simple, honestly. During Sonic Adventure 1, when being brought to the past by Tikal's spirit, one of the ways Sonic and Tails could have changed history is by kicking Tikal's dad's ass before he could attack the Master Emerald's shrine, and then... Yeah, they could just have fucked Tikal.
Imagine Knuckles's surprise in the present when he blinks and suddenly all his people are back, but they all look a little bit like Sonic and/or Tails. Or the Echidna city is still there instead of turning into the Mystic Ruins, but there are statues and murals of weirdly-shaped blue hedgehogs and multiple-tailed foxes. 
