Hello. Rusted Moss now has unofficial multiplayer, allowing you to play with your friends, with a few limitations. This guide will explain how to install the mod, what the settings do, how to invite your friends, and answer some FAQs.

Let's get started!

Update June 9 2025: If you had connection issues, try the latest version (1.5+).

The mod behind all of this is Ghost Multiplayer. It uses a perversion not known to the Ancient Ones to access the Steam API and broadcasts your player position (and some other boring garbage) to anyone who joins your game, without modifying any* of your game's state.

In English, you are haunted by the ghosts of Fern past, animated by your closest friends. These ghosts cannot interact with your world, and you cannot interact with theirs.

To play, everyone needs a legal copy of the Steam version of Rusted Moss, and each player needs to be friends with everyone else (probably).

To install the mod, you'll first need to install Rusted Moss Mod Manager (RMMM), then install Ghost Multiplayer using RMMM's interface in-game. You can either follow the instructions on the RMMM Github page[github.com] and figure it out, or use this nice step-by-step guide.

1. Go to releases page[github.com] on the RMMM Github repository.
   
2. Find the latest release (at the top of the page) and expand the "Assets" tab.
   
3. Download the .zip file ("rmml_X_XX.zip").
   
4. Open the zip file. Inside you should see 3 files (meta_info, modlist, and rmml) and a folder (rmml).
   
   Now, we need to locate the steam directory so we can install RMMM.
   
   
5. Open Steam, and right-click Rusted Moss.
   
6. Choose "Manage", and then "Browse Local Files". This will open the file explorer into the "Mose" folder. Inside, you'll find the Fern_custom folder (for modifying Fern's palette), the data.win file (for modders), and the "mods" folder (which we're after).
   
7. Open the "mods" folder.
   
8. Copy the files from the RMML zip file into the "mods" folder, replacing "meta_info".
   
9. Verify that the folder looks correct. You should have a folder called "rmml" inside the "mods" folder.
   
   RMMM is now installed! Now for the fun part.
   
   
10. Start Rusted Moss. You might hear a short "ding", this is normal.
    
11. In the top right, you should see a gear icon. If you do not, RMMM was not installed properly.
    
12. Press the gear icon to open the RMMM menu.
    
13. Click on the "Browse Mods" tab to open the browse menu.
    
14. Click "Download Manifest". This fetches the latest list of Rusted Moss mods from the database Github[github.com].
    
15. From here, you can use the "Download" button to download any mods you want to use and use the wide arrow buttons at the top and bottom or the mouse scroll wheel to see more mods.
    
16. For now, download "Ghost Multiplayer".
    
17. After it downloads, go back to the "Installed Mods" tab.
    
18. Click the empty box on the left next to "Ghost Multiplayer" to enable the mod. Any other mods you want to use must be enabled in the same way.
    
19. Finally, use the "Save & Quit" button to exit Rusted Moss.
    
    Ghost Multiplayer is now enabled!
    
    
20. To make sure it's working properly, restart Rusted Moss. You might hear a longer "ding" than before, this is also normal.
    
21. Underneath the RMMM gear icon, there should be a grayed-out Fern icon. Clicking on it opens the Ghost Multiplayer menu. If you don't see it, make sure you enabled the mod with RMMM.

Now that you've installed Ghost Multiplayer, how do we play with friends? The short answer is one player presses "Create Lobby" to make a lobby, then uses the "Invite Friends" button to invite other players. To accept an invite, you must be in-game with the mod installed. When you join a lobby, your name will appear on the Ghost Multiplayer menu.

If you are having issues connecting to a lobby, check out the FAQ below.

Once in a lobby, you can open a save and play the game normally. If you are in the same room as another friend, you will both see each other and can communicate using the emote wheel (defaults to "O"). If you open the map, you will see an icon for each player in the lobby.


Ghost Multiplayer has a few options to customize the experience.

• "Palettes": When enabled, you can see your friend's palettes and your friends will see yours. If disabled, ghosts in your game and your ghost in your friend's games will use the default palette(s). If you have lag spikes whenever a player starts a save, disabling this option can help.
  
• "Map Icon": When enabled, ghost players will appear on the map. You cannot hide your location from other players. Negligible performance impact.
  
• "Names": When enabled, each player's Steam name will be shown above their ghost. Disabling can improve the performance when multiple ghosts are in the same room.
  
• "Off Icon": When enabled, an off-screen icon will appear when you are in the same room as a ghost, pointing you to the ghost.
  
• "Hookable": When enabled, ghost players will be hookable.
  
• "Fast/Safe Packets": This setting toggles between the type of network packet. Safe packets increase latency, but are more likely to reach distant users. If you have connection issues, having each player enable Safe Packets can help.
  
• "Emote": Clicking this lets you rebind the emote button. Holding the emote button opens a wheel, similar to selecting a weapon, and releasing will send the emote to other players.

Clicking on the version number on the bottom right enables a debug renderer, which can help diagnose issues.

Below are a list of FAQs and common issues.

The ghost players don't have any hair. This intentional.
The short answer is boring technical reasons. The longer answer is that making interactive multiplayer would likely require a complete rework of most of the game's systems, a task I am largely uninterested in undertaking. If you are interested in the challenge, come find me in the Rusted Moss Discord, and I'll share my secrets.

Before doing anything else, try updating Ghost Multiplayer. I might've fixed your issue already.
You must be in-game to accept invites. Additionally, I recommend waiting a few seconds for the game to fully load before accepting an invite.
Make sure that everyone has everyone else friended on Steam. If it still persists, try having everyone restart Rusted Moss.
If you find an issue, let me know in the comments of this guide, or message me on Discord (Harlem512), or open a Github issue on the mod-database repo. If the issue is "I/my friend can't connect", I probably can't help you (steam API moment), but I'd still like to know. You can also use the debugger.

To enable debug logging, click on the version number on the Ghost Multiplayer menu. There are 3 sections.

• Top Left: On the top left is a list of all player in the lobby (except yourself). If any player names are a bunch of numbers, then the steam API failed to fetch their steam name. If a player is in the lobby but not in the list, then there is a fatal syncing issue and you should let me know.
  
• Bottom Left This is a log of (most) events in the game, including any warnings or errors. If you see any errors, let me know.
  
• Top Right: This is the network status for each player. There are two types here: you (labeled "SELF") and other peers (labeled with their steam name)
  
  • SELF: Your outgoing network status. The 4 numbers are explained in order:
    
    1. Time since last sync packet. If you are in a save file (ie not in a menu) this number should hover around 10.
       
    2. The current internal character id (0 fern, 1 maya, 2 ameli). If this is out of sync with the character you are playing, return to the menu and load the save file again.
       
    3. If the player fell. This is 1 immediately after the player falls or respawns and 0 otherwise. If your ghost is teleporting around and this is 1, let me know.
       
    4. The current room id. This is compared against other ghosts to determine if rendering should happen/
  • Peer: All other players in the lobby will have these 4 numbers:
    
    1. Time since last packet. This number should hover around 10, assuming that player is in a save file (not in a menu). If that player is moving around, but this number keeps increasing, then there is a connection issue between you and that player.
       
    2. Time between packets. This is how long the last packet took to arrive. This should also be around 10.
       
    3. Ghost room id. This is the room id where the ghost is. If this id matches the room id for SELF, then the ghost will render. If this number doesn't change even though the time since last packet is correct, let me know.
       
    4. Character. This is the character id (0 fern, 1 maya, 2 ameli) for the ghost player. If this is out of sync, have that player return to the main menu and load their save again.

Ghost Multiplayer wouldn't be possible without a lot of things (katsaii's Catspeak, the devs enabling the cheaty Catspeak secret mode, etc), but it would be impossible if I wasn't shown the dark arts by Mr L. So go check out the Archipelago randomizer mod[github.com] and get away from me.

As always, you're now playing with mods. Please don't message the devs asking for help, message me instead.

Use the Archipelago randomizer to play co-op. Play hide-and-seek. Show your friends how to do jumps. Race each other to the final boss. Cringe at bad plays. And, most importantly, have fun!