Super Mario Bros. 2
UntestedNES · 1988 · Platformer · Decompilation
Pull up vegetables and throw them at Shyguys across seven dream worlds.
Controls
| Arrow keys | move, duck, climb |
| X | A (jump) |
| Z | B (run, pick up, throw) |
| Enter | Start |
| Shift | Select |
| Gamepad | supported through EmulatorJS |
About this build
Super Mario Bros. 2 reassembled byte-for-byte from the Xkeeper0 disassembly and run in the browser. The project ships only 6502 source and a loader page: you supply your own cartridge dump, which is read in the page and never uploaded. The build reproduces the (USA) (Rev 1) ROM body exactly — 0 of 262,144 bytes differ — and can also produce the earlier US revision and the Japanese Super Mario USA.
- Built from
- The Xkeeper0 6502 disassembly, reassembled with asm6f, run on EmulatorJS 4.2.3 with the libretro fceumm core (nestopia selectable).
- Type
- Decompilation
- Game files
- You supply your own Super Mario Bros. 2 (USA) (Rev 1) ROM; it is read in the browser and never uploaded. ROM body sha1 ff5bcacf7417b4de1c49f9e54c2905d91391455b (262,144 bytes; a 16-byte iNES or NES 2.0 header on top is fine). The earlier (USA) revision and Super Mario USA (Japan) are recognised and will run too.
- Code licence
- The upstream disassembly carries no licence file. The vendored EmulatorJS is GPL-3.0 and the libretro fceumm and nestopia cores are GPL-2.0.
- Assets
- No game assets are distributed. Super Mario Bros. 2 is © Nintendo.
- Source
- Xkeeper0/smb2 ↗
What has been tested
Reassembly byte-matches the (USA) (Rev 1) ROM body (0 of 262,144 bytes differ; the 3 differing file bytes are all iNES vs NES 2.0 header). In the browser: boots from a user-picked ROM with zero off-site requests, reaches actual level play rather than the character-select screen (StackArea = $C0), and the controller demonstrably drives the player — from one save state, holding Right and holding Left move PlayerX in opposite directions from byte-identical work RAM. A save state survives a page reload with position, hearts and lives intact. All runs muted.
Last tested 2026-10-05 in Chrome (headless, Linux). Full playthrough: not verified. How games are tested.
Known limitations
- Not hosted: the upstream repository carries no licence file.
- Not yet playable here: no hosted page has been published for this title.
- Progress is a save state, not a battery save — Super Mario Bros. 2 has no save feature of its own.
- Verified to survive a page reload. Surviving a full browser restart was not verified.
- Gameplay was verified from the game's own RAM on the fceumm core only; nestopia was verified to boot and render, nothing more.
- No level was cleared during testing, and only World 1-1 was reached. Later worlds, bosses and the ending are untested.
- Only Mario was played; the other three characters are untested.
- All testing was done muted, so nothing is known about audio.
- Keyboard and gamepad mappings are untested: the tests drive the emulator's input API directly.
- Tested only in headless Chrome on Linux. No headed browser, no mobile, no touch controls.
Saves
The cartridge has no battery, so there is nothing for the game itself to save. The page keeps an automatic save state in this browser's storage, keyed by your ROM's SHA-1, written every 15 seconds and when you leave the page, and restores it next time. Clearing site data removes it; there is a button in the footer to discard it.
