Nintendo's resurrected Star Fox 2 has become the subject of newfound attention this week thanks to the announcement that the lost game will be included in the Super NES Classic Edition later this year, bringing it out of the vault more than twenty years after development ended. Fans have been able to sample it for years thanks to a leaked unfinished version of the game that appeared online during the height of excitement for emulating Super NES games in the wild west era of the Internet, but aside from generally knowing that this early version is out there, it's unlikely that most of Star Fox 2's new fans are aware of the long path that the game traveled from Nintendo's vault to the open Internet. Nobody just shoved a cartridge into a modem and called it a day. SNES Central takes a look back at how that rogue copy of Star Fox 2 escaped into the wild.
The real blockbuster, which served as the pinnacle of the SNES emulation scene, in my opinion, was the release of the final beta of Star Fox 2 in August 2002 (well documented by d4s in this FAQ, who also had a big hand in the discovery of the ROM image). The first screenshots appeared on the now defunct website, sportkompaktwoche.de. The ROM itself needed several fixes (made by The Dumper) before it could play in emulators, though there were accusations that it was a fake before that happened. The unfixed ROM was leaked by "skyhawk" of the German fan translation site, Alemanic Translations. Apparently skyhawk claimed to have found this game on a prototype cart and dumped it himself, probably leading to the widespread belief this game was found off a prototype cart.
In reality, Star Fox 2 was leaked as a pure assembled binary from a former developer who wanted the game emulated, and the ROM was not in a proper SNES ROM format initially. There was no source code leaked, nor was there ever a prototype or production cart of it. Soon after the leak of Star Fox 2, emulator authors incorporated proper Super FX emulation, allowing the general community to play the game in all its glory.
Before fans could play this version of Star Fox 2, it had to be patched and manipulated to make it playable in the emulators of the day. Fan translation groups reworked the script into English. Even the lingering debug tools had to be disabled to make the game as much like the presumed finished release as possible. Even this version isn't truly the final game though, as Retronauts reports that Star Fox 2 designer Dylan Cuthbert has noted that the true mastered version has never leaked.
According to programmer and designer Dylan Cuthbert, a completed build that's never been leaked (and will presumably be the version included with the Super NES Classic Edition) received an extra coat of polish and incorporated a greater deal of randomization to add even more replay value to the experience. The planned multiplayer mode is also hopefully in working order, and maybe they even assigned some greater purpose to the giant coins bearing General Pepper's likeness which you can find hidden around the game.
Officially releasing Star Fox 2 isn't the end of the legend, it's just the next chapter. The Super NES Classic Edition releases in September 2017.