How to fix to the 'Sonic vs Infinite' scene: it starts with Tails and some people (Mobians, to be precise) being surrounded by some robots. Tails tells the people to get to safety (which they do after a few of them worry about his safety) and pulls one of his weapons out. However, Sonic steps in to save the day before the two-tailed fox could do anything. Sonic asks Tails if he is alright, to which he responds, "I'm fine, though I could have handled these robots myself".
Sonic (not teasingly) chuckles and (in the same style as the original cutscene) turns to face Eggman, who announces his newest creation which, to Sonic and Tails' surprise, is not a robot this time. Sonic charges at the new enemy, only for him to step out of the way. Tails, initially believing the enemy to be faster than Sonic, decides to scan him. But the readings (as we can see here) are indecipherable even for an 8-year-old genius.
Sonic gets beaten around by clones (Shadow, Metal Sonic, Zavok and Chaos) and Tails, instead of standing there and doing nothing, decides to join the fight, ignoring Sonic's protests and objections. Tails is intercepted and beaten by the new enemy, but the fox is not ready to give up just yet. He repeatedly, yet unsuccessfully, tries to save Sonic and gets temporarily knocked out. Sonic tries to get to Tails, but the blue hedgehog winds up getting badly beaten up. With his body on the ground and the stretch of his hand reaching out towards his little brother, Sonic calls out his name and faints.
Tails wakes up to find the new enemy carrying Sonic and, in his terrible condition, tries to stop the group of enemies and go after them. But it was already too late. Unable to fly properly, Tails sees the group of enemies take to the sky and disappear in a flash of light. With tears in his eyes, Tails painfully calls out Sonic's name, having lost his big brother. We then see glimpses of Eggman taking over the world, with people (including Team Sonic) unsuccessfully trying to win and eventually losing hope.