You can easily play Samurai Gunn online using Parsec

[ClashDev]

Parsec is game-streaming software that allows you to play local-multiplayer games online. It works amazingly well and it's easy to set up. Here's some info on how to get started: https://youtu.be/6VBJf0C_JjE?t=54s
There's a whole Parsec community too that regularly plays games like this online. Lag is not an issue depending on your internet speeds and distance from the hosting player. I even played a 7 player Towerfall match and it was playable despite the host only having 10 upload speed (that's low).

You can join the Parsec Discord server to find players: https://discord.gg/MjW84vP

[JP - Ardamaeus]

Hey man we tried running the game on parsec and guests joining aren't having their inputs recognized.

How did you set up the game when you played it on parsec? Do you have to go into the controller settings and set all 4 to xbox360 inputs?