After nearly a year and a half of work, a small team of modders released a multiplayer mod for The Legend of Zelda: Breath of the Wild this week, fulfilling a $10,000 challenge set out by YouTuber PointCrow in November 2021. The mod, which is now available via Discord, makes it possible for up to 32 players to galavant around Hyrule together, sharing progress and competing in some custom game modes added with the mod. Lead modder AlexMangue tells me PointCrow, who regularly speedruns and makes videos about Breath of the Wild, has been a big part of the mod's development.
"He didn't just put the 10K bounty. He has been supporting us monetarily throughout the project in addition to the 10K bounty," AlexMangue says. "Also, he was in some way the director of the project in the way of him doing the creative side of it, like bringing us ideas on what to work on next."
So far, the mod is able to sync an impressive number of things between players, including player location, weather and time of day, enemy health, and progress through discovered towers and shrines. It is still missing some key features to feel fully complete, though, like syncing enemy AI. In the mod's current form, other players will be able to tell when you've damaged an enemy, but it won't be doing the same thing on their screen as it is on yours. This discrepancy highlights the challenge of pulling off a mod like BotW Multiplayer when access to the game's code isn't really available.
"We didn't really use the game code on its own a lot as Nintendo ships them without any symbols and therefore it is not really readable, so we had to do some hacky things to make it work," says AlexMangue. "The main part of this is similar to how cheaters work on other games. We inject our own code into the emulator and therefore have access to the information saved on the RAM of your computer for the emulator process. With this, we look for certain information in the memory such as player's position, rotation, etc. This is the extraction part of it, just obtaining the data needed to send to a server we coded.
After the server obtains the data from each player, it then analyzes part of it and relays it to the other players. Here's where the hacky thing starts. We are actually using NPCs from the game and making them look like Link. After we spawn them we just look for the same information we looked at before but for our NPCs and with this we change their position, rotation, etc."
Some of Breath of the Wild's code is naturally easier to parse from system memory than other bits. Enemy health is a simple value, for example, while AI is naturally much more complicated. The modders have a Trello project with more planned features, though AlexMangue says there are some priorities after this 1.0 release, including making it possible to sync progress on main quests.
Getting it that far has been a major team effort, with development work by modders Ahrdoc and Sweet, as well as contributions from a number of other established Breath of the Wild modders. For that core team, though, this week's release was a particularly big moment. "This is actually the first release anyone on the team has done so it was super cool," AlexMangue says. "So happy to see how cool the community is, a lot of people helping each other."
Installing the mod is a pretty complex process, including getting Breath of the Wild running in Wii U emulator Cemu (the Switch version of the game is not supported), patching the game and connecting online. Players in the mod server have helped make at least one part of the process easier by spinning up servers that anyone can play on without hosting one on their local machine. If you're brave and eager, dig into the install guide here.
Otherwise, here's a fun German YouTuber's video of the mod, playing its custom hide and seek game mode with a posse of five other players.