This week, twitter user Biggestsonicfan, in an extended Twitter thread, made waves by laying out the way a number of hidden characters in the original arcade version of Fighting Vipers are referenced (and in one case, accessed), and reminding us that Sonic and Tails are hiding just slightly beyond the Character Select.
Before we continue, let’s be clear:
This is not entirely newfound information. Forums and sites such as The Cutting Room Floor wiki have info on Sonic’s hidden cameo going back years, but what BiggestSonicFan has shared in the thread is a straightforward explanation of what is happening to surface these characters.
Further, this is also not a method to unlock Sonic or Tails in the arcade, Saturn, or Xbox 360 versions of the game. This is merely a bit of a code discussion (and a reminder that AM2 once hid Sonic in a rather unlikely place).
Fighting Vipers’ character select screen is built on an array of eight values, one for each character. By fulfilling specific and demanding requirements, the game will extend the array by 1, letting you play as the otherwise hidden ninth entry in the array, “Mahler.” However, there is yet another inaccessible 10th entry in that array which instructs the game to play as Sonic (with Tails as an alternate costume for Player 2).
There isn’t a way to actually select and play as Sonic from within the game itself, but YouTube poster TrackerTD show off a playable Sonic by manipulating the array length value via PC emulation in this 2016 video.
The year after Fighting Vipers hit arcades, AM2 would go on to release Sonic the Fighters, which contains unsurfaced character data for a cat version of Honey from the Fighting Vipers series, and Fighters Megamix on SEGA Saturn, which includes Bark and Bean as unlockable characters.