Two modders who call themselves MrBean35000vr and Chadderz (and who are also brothers) have released a video demonstration of their upcoming mod for New Super Mario Bros. Wii which enables online multiplayer inside the game.
They first note that their mod is different to Dolphin Netplay, which is a way to play the game’s local multiplayer over the internet – their mod is proper online multiplayer.
Further, they have said that the mod, while limited to New Super Mario Bros. Wii at the moment, should also work with other Wii games with local multiplayer only when finished, although some may need specific patches for it to work. It may even work with Game Cube, Wiiware, and Virtual Console games in the future.
However, there are still multiple issues with the mod at the moment, which is why they’re only previewing it and not releasing it publicly. When it is ready, it will be released with the source code so others can add to it.
Here’s how it works, in their words: “It works by sending a long stream of inputs over the Internet; button presses on a controller. An assigned host dictates RNG (random number generator, random elements in games like which item you get from a box in MKW for instance), and synchronises level loads so that everyone plays the game at the same speed. It also has an adjustable lag threshold, to allow smoother gameplay with people far away with you, at the cost of slight input delay.”
To get the mod running, you’ll need Wii or Wii U for each player, an internet connection, and a Homebrew Channel. If you want to host, you’ll also need to have a working knowledge of how IP addresses and port forwarding works. Although, the modders do note that there may even be a matchup service that eliminates this need further down the line. However, they also pointed out that you won’t be able to play with people in a different region or with a different version of the game than you.