Sonic the Hedgehog 2
Boots, lightly testedMega Drive · 1992 · Platformer · Decompilation
Tails joins in, the spin dash arrives, and Emerald Hill sets the pace.
Controls
| Arrow keys | move |
| Z / X / C | A / B / C (any jumps) |
| Enter | Start |
| Gamepad | standard mapping |
About this build
Sonic the Hedgehog 2 reassembled from the sonicretro/s2disasm disassembly, byte-identical to the cartridge, and run in the browser on mdcore, this project's own MIT-licensed Mega Drive core. You supply your own ROM: it is read in the tab and never uploaded.
- Built from
- the sonicretro/s2disasm disassembly, reassembled to a matching ROM and run on mdcore, an MIT-licensed Mega Drive core (WebAssembly)
- Type
- Decompilation
- Game files
- Your own Sonic the Hedgehog 2 ROM (1,048,576 bytes). Rev B from the Sonic Classics compilation, sha1 2af1003247aec262089c8df22d05e80d04a1b5e4, is the one tested; REV01, sha1 8bca5dcef1af3e00098666fd892dc1c2a76333f9, is also recognised. Nothing is uploaded.
- Code licence
- mdcore is MIT; sonicretro/s2disasm is unlicensed research. See web/THIRD-PARTY-NOTICES.txt.
- Assets
- None distributed — the player supplies their own ROM
- Source
- andrewnakas/sonic2-web ↗
What has been tested
Rev B reassembles byte-identical to the Sonic Classics image once the retail header checksum (two bytes) is restored; REV01 passes upstream's bit-perfect check. In the browser, muted: the ROM was read through the page's file picker with a matching sha1, booted through the SEGA and title screens into Emerald Hill Zone, and Sonic ran right under keyboard input with rings and the HUD counting. No page errors and no off-origin requests.
Last tested 2026-10-08 in Edge (headless, muted). Full playthrough: not verified. How games are tested.
Known limitations
- Requires your own ROM; none is provided.
- Sound is on by default (the Sound button under the game turns it off); it was measured, not listened to.
- Verified only as far as running through the start of Emerald Hill Zone. Later zones, bosses, special stages and two-player mode have not been play-tested.
- mdcore was tuned against Sonic 1; small timing differences from real hardware are possible.
- No on-screen touch pad.
Saves
Sonic 2 has no battery save, and this page keeps nothing in browser storage — your ROM is asked for again after a reload.
