Tennis is a game designed for two players, but the Virtual Boy, Nintendo's much maligned stereoscopic system, was a solo experience.

From the Nintendo Entertainment System to the Switch, every other Nintendo console supported two-player modes, but the Virtual Boy, an isolating gadget that you stuck your face into like a virtual reality headset, never got a multiplayer mode, despite Mario Tennis being one of its few notable games.


That is until last week, when a modder released a two-player patch for Mario Tennis. With the patch and two Virtual Boys with two copies of the game connected via a standard Category 5 cable, a two-player mode for the system is finally here.

As mentioned on the Planet Virtual Boy forums, the multiplayer patch allows for head-to-head competition in singles and doubles matches. Playing doubles on the same team, however, is a work in progress.

Fans have always speculated this multiplayer mode could happen, ever since a listing for the GameLink Cable appeared in the short-lived device's instruction manual. Sadly, the Virtual Boy went bust before the cable made it to market.

"I wanted to find out once and for all if there was any multiplayer code left," Virtual Boy hobbyist developer Martin Kujaczynski, aka M.K., told me in an email.

The trouble was knowing where to look. Mario Tennis is written in around 30,000 lines of assembly code. Discovering a few lines of multiplayer code in that ancient tome would be like finding a needle in a haystack. To help him hone in on the right areas, he used a modified emulator to rule out extraneous data like music and graphics. This narrowed the search down to 3000 lines, making it more like finding a needle in an unfamiliar Wal-Mart.

Sure enough, he saw what looked like instructions for the Virtual Boy's link port. With the aid of the homemade cable, all he had to do was get the code up and running.

"The time consuming part was figuring out what the unused code does and how to use it," said Kujaczynski.