works on my PC fine for ages now - here's some instructions - somehow figure out how to do it on the Pi, shouldn't be much harder...
SNES Netplay On Windows
First you’ll need to grab a few files:
RetroArch and the LibRetro cores
Phoenix launcher for RetroArch (not necessarily needed, but makes things way easier)
Once downloaded, unpack all of the files. Typically, you’ll want to toss the contents all in the same folder for easier access.
Launch the Phoenix loader.
Once the Phoenix loader is loaded up, You’ll need to make a few adjustments. First up is the RetroArch path option.
Set that retroarch.exe which was located inside the RetroArch zip file you extracted.
For SNES games, set the libretro core path to snes9x_next_libretro.dll that was inside the cores zip file.
RetroArch supports a ton of different emulators, although not all support NetPlay.
Player 1 will need to start the server. To do so, check the Netplay checkbox and set the radio button to Server on player 1’s machine.
Player 2 will also enable the Netplay option, but select Client.
The client now needs to set the Host IP field. Here, enter the IP of payer 1’s server.
For smooth play, set the Delay Frames option. This will vary based on your bandwidth, but we have had the best luck with this set to 4.
Your mileage may vary. For slower internet connections, you may want to set it a bit higher.
Next up, be sure that port 55435 is open and forwarded on your router. If you’re not sure how to forward ports, check out portforward.com.
Next up, you need to select the SNES ROM that you want to play. Both players should have the exact same ROM if possible for smoothest play.
Different copies of the same game will sometimes work, but I can’t guarantee anything with that.
In the Normal ROM Path field, browse to your ROM file on both the client and server machines.
You’re all ready to go (with the exception of your controls which can be configured using Settings>Input. On the server computer (Player 1), click the Start RetroArch button.
Once the server is launched, do the same on the client (Player 2). You should now be playing together!