: You simply provide your legal Sonic 3 & Knuckles ROM file from Steam to the Sonic 3 AIR software, and it rebuilds the game with 16:9 support, 60fps menus, and achievements.

Sonic the Hedgehog 3 and Sonic & Knuckles are widely considered the pinnacle of 16-bit platforming. Originally released as two separate Sega Genesis cartridges in 1994 due to time constraints and production costs, these games were always meant to be a single, cohesive experience. While Sega later offered the "Lock-On Technology" via the Sonic & Knuckles cartridge to combine them, the final product still suffered from minor bugs, inconsistent music choices, and cut presentation elements.

Once you have successfully created your patched ROM, you can play it. Because Sonic 3 Complete is designed for the original 16-bit hardware, it can be played on a real Genesis using a flash cart, or on virtually any Sega Genesis emulator on platforms like PC, Mac, Android, and even modded 3DS systems. If you are playing on a real console, do note that some emulators may have compatibility issues—for example, jEnesisDS on the Nintendo DS only supports ROMs smaller than 3MB, which S3C exceeds.