To play on Android, you generally need a Sega Genesis emulator because the game is a fan-made "hack" or modification rather than a standalone Android app. Option 1: Using an Emulator (Traditional Method)

A pre-packaged Android application package (APK) that wraps a Sega Genesis emulator and the pre-patched Sonic 3 Complete ROM into a single, installable file.

This version is widely considered the "definitive" way to experience the 16-bit classic due to its deep customization and bug fixes.