It’s already in and has been since launch. Go to NETWORK, HOST/JOIN GAME, and then the room code panel is top-right of the game page: one of you hosts, the other pastes the code. Rules are in the FAQ. P2P only, so you need to ask someone rather than have matchmaking.
Honestly the netcode wasn’t the hard part, because Ikemen GO already has it. It just expects a normal network connection, which browsers don’t give you. So the real job was plugging a browser-to-browser connection in underneath it — the game never knew the difference. Players connect straight to each other, no server in the middle.
The annoying parts were around it, not in it:
Two browsers can’t just find each other. They have to swap connection info first. Mine was copy-pasting a huge string into Discord at one point. Now a small cloudflare server does that swap so you only share a short room code. Some routers still won’t connect directly, so there’s a relay for those. Both players have to be running the exact same files or it desyncs instantly. The build checks that and shows a Build ID — if yours don’t match, don’t bother starting. Delay netcode works well. Rollback’s in there but it’s experimental.
If you want it on yours: ship one fixed build and don’t let players add their own characters. Then everyone on your page matches automatically. Do not ship studio-lite. Use Studio and Command Prompt to make your uploadable build.
I caught an error that might mess with build ID’s. Please update to the latest version.