Elden Ring Seamless Co-op

Install the Seamless Co-op mod on a Steam Deck and play through the entire game with a friend.

Install the Seamless Co-op mod by LukeYui on a Steam Deck. This lets you play through the entire game cooperatively — no summoning pools, no fog walls, no sending your friend home after a boss.

Prerequisite: SSH access to the Steam Deck makes most of these steps much easier. Only one step requires Desktop Mode.

Overview

1. Download the mod
2. Extract it into the Elden Ring Game/ directory
3. Configure the password and settings
4. Add the mod launcher as a non-Steam game and force Proton (requires Desktop Mode)
5. Disable Elden Ring auto-updates

1. Download the Mod

Download from either source (same files):

• Nexus Mods: nexusmods.com/eldenring/mods/510 (Manual Download)
• GitHub: LukeYui/EldenRingSeamlessCoopRelease

Over SSH, you can download the latest release directly on the Deck. Check the GitHub releases page for the current version, then:

# Replace the URL with the latest release link
curl -LO "https://github.com/LukeYui/EldenRingSeamlessCoopRelease/releases/download/v1.9.5/Seamless.Co-op.v1.9.5-510-1-9-5-1772481623.zip" -o /tmp/ersc.zip

2. Extract into the Game Directory

The mod goes into the Game/ subfolder — not the Elden Ring root.

ELDEN_RING="$HOME/.local/share/Steam/steamapps/common/ELDEN RING/Game"

# Verify the path exists
ls "$ELDEN_RING/eldenring.exe"

# Extract
unzip /tmp/ersc.zip -d "$ELDEN_RING"

After extraction, you should have:

Game/
├── ersc_launcher.exe
└── SeamlessCoop/
    ├── crashpad/
    │   └── crashpad_handler.exe
    ├── locale/
    │   └── english.json
    ├── ersc.dll
    └── ersc_settings.ini

3. Configure the Mod

Edit the settings file:

nano "$ELDEN_RING/SeamlessCoop/ersc_settings.ini"

Key settings:

You can set the password over SSH without a text editor:

sed -i 's/^cooppassword =.*/cooppassword = YOUR_PASSWORD_HERE/' \
  "$ELDEN_RING/SeamlessCoop/ersc_settings.ini"

The co-op save (.co2) is separate from your normal save (.sl2), so your solo progress is safe.

4. Add as a Non-Steam Game (Desktop Mode required)

This step requires the Steam UI — it can’t be done over SSH.

1. Switch to Desktop Mode (hold Power > Switch to Desktop)
2. Open Steam
3. Click Add a Game (bottom-left) > Add a Non-Steam Game
4. Click Browse, navigate to ~/.local/share/Steam/steamapps/common/ELDEN RING/Game/ and select ersc_launcher.exe
5. Right-click the new library entry > Properties > Compatibility
6. Check “Force the use of a specific Steam Play compatibility tool”
7. Select Proton 8.0 (or Proton 9 / Experimental — all work, 8.0 is most stable)

Without forcing Proton, the launcher will try to run as a native Linux binary and fail.

If using other mods alongside Seamless Co-op, add this to Launch Options:

WINEDLLOVERRIDES="dinput8.dll=n,b" %command%

5. Disable Elden Ring Auto-Updates

The mod breaks every time FromSoftware patches the game. Only update when a new mod version is available.

In Steam: right-click Elden Ring > Properties > Updates > “Only update this game when I launch it”

This way, always launch via the mod’s ersc_launcher and the base game won’t auto-update out from under you.

6. Import Your Existing Character (Optional)

The mod uses a separate save file. To bring over your character:

# Find your vanilla save
find ~/.local/share/Steam/steamapps/compatdata/1245620 -name "ER0000.sl2" 2>/dev/null

# Copy it as a co-op save into the mod's prefix
# (the exact path depends on the non-Steam shortcut's app ID)
cp <path-to-ER0000.sl2> <co-op-prefix-path>/ER0000.co2

Playing

Once everything is set up, launch the game from the Seamless Co-op launcher in your Steam library (not the regular Elden Ring entry).

In-game items added by the mod:

Updating the Mod

When a new version is released:

ELDEN_RING="$HOME/.local/share/Steam/steamapps/common/ELDEN RING/Game"

# Back up your settings (password, scaling, etc.)
cp "$ELDEN_RING/SeamlessCoop/ersc_settings.ini" /tmp/ersc_settings.ini.bak

# Remove old version
rm "$ELDEN_RING/ersc_launcher.exe"
rm -rf "$ELDEN_RING/SeamlessCoop"

# Download and extract new version (update the URL)
curl -LO "https://github.com/LukeYui/EldenRingSeamlessCoopRelease/releases/download/<version>/<filename>.zip" -o /tmp/ersc.zip
unzip /tmp/ersc.zip -d "$ELDEN_RING"

# Restore your settings
cp /tmp/ersc_settings.ini.bak "$ELDEN_RING/SeamlessCoop/ersc_settings.ini"

# Clean up
rm /tmp/ersc.zip /tmp/ersc_settings.ini.bak

Your save file and the non-Steam game entry are unaffected.

Troubleshooting