Sonic 4
There’s an Intro section on the official Sonic 4 website now with the background story of Sonic 4. There’s no direct link, but click “Intro” under “Game Info” on the upper left of the site to see it. The site recaps the story for Sonic the Hedgehog, Sonic 2, Sonic 3, and Sonic & Knuckles.
Basically, the story is that in Sonic 1 Dr. Eggman turns animals into robots on South Island in an attempt to collect the Chaos Emeralds. Sonic defeats Dr. Eggman in Final Zone. Then, in Sonic 2, Dr. Eggman tries to create the Death Egg. Sonic and Tails fight him on West Side Island and the Death Egg, defeating him. Immediately after, in Sonic 3, the Death Egg falls on Angel Island, which was floating in the air, causing it to crash into the sea. Angel Island held the Master Emerald. Knuckles steals the Chaos Emeralds because Dr. Eggman convinced him that Sonic was after the Master Emerald. Dr. Eggman repairs the Death Egg, but Sonic and Tails blow it up again. It crumbles back down on Angel Island. Finally, in Sonic & Knuckles, Dr. Eggman has EggRobo attack Knuckles because he no longer needs him. Dr. Eggman then steals the Master Emerald and launches the Death Egg again. Knuckles pursues EggRobo, and Sonic pursues Dr. Eggman. Sonic saves the Master Emerald and returns it to Knuckles and Angel Island, allowing the island to float again. Now Dr. Eggman prepares to fight Sonic once more.
For anyone who cares about the Sonic story (which most likely isn’t anyone reading this), this is interesting for a few reasons. It seems that the Sonic 4 story is disregarding every game besides Sonic 1,2,3, and S&K. Also, there’s no mention of the Super Emeralds. There used to be confusion about why Knuckles thought Sonic took the Chaos Emeralds when they hadn’t been on Angel Island, but they took that part out as well. It’s the simplest explanation and is what I expected, but it’s interesting to see it.