Super Smash Bros. Melee

Super Smash Bros. Melee is a 2001 platform fighter game developed by HAL Laboratory and published by Nintendo.

Slippi

You can use the slippi-nix flake to declaratively install and configure Slippi with Nix, or get the AppImage directly from Slippi's website.

If you are using the Appimage, to run Slippi Online or Slippi Playback you will need libcurl.so.4 to be in your appimage-run packages. This can be easily added through a package like curlMinimal.

  programs.appimage.package = pkgs.appimage-run.override { extraPkgs = pkgs: [
  	pkgs.curlMinimal.out
  ];};

The configuration to setup Appimage support and specifically the Slippi Appimage would look like the following

{
  programs.appimage = {
    enable = true;
    binfmt = true;
  };
  programs.appimage.package = pkgs.appimage-run.override {
    extraPkgs = pkgs: [
      pkgs.curlMinimal.out
    ];
  };
}

Which is just the snippet from Appimage#Configuration with the needed library added to the appimage-run package.

B0XX Emulation

B0XX controller emulation can be done via keyb0xx. A Nix package for keyb0xx can be found here.