GungeonTogether

This experimental continuation is based on the original GungeonTogether project by lam and contributors. It remains available under the included MIT License.

GungeonTogether is a multiplayer mod for Enter the Gungeon that allows online co-op play using Steam P2P networking.

The current session size is three players: one host and up to two clients.

Modded sessions are supported when every player uses the same BepInEx plugins, plugin versions and registered ModTheGungeon items. Incompatible clients are rejected with the first detected manifest difference.

Version 0.10.8 smooths remote players by preserving the sender's original 30 Hz movement timeline even when Steam delivers several packets in one frame. Its adaptive interpolation buffer reacts to real packet jitter without imposing the old fixed delay, while the physical proxy uses smooth velocity correction.

The mod uses the game's native co-op door, sealed-room and elevator rules and feeds the native camera the whole three-player bounding box. The host relays complete inventory snapshots (guns, ammo, passive items, active items and current weapon), making drops, missed events and reconnects self-healing. Ground pickups, shared money/keys and pickup claims remain host-authoritative. Inventory changes are sent reliably and removals are confirmed by a fast second revision, preventing stale packets from undoing a new pickup. Transaction IDs make world mutations idempotent, while host-session and floor-epoch stamps reject delayed gameplay packets from an earlier floor.

From the main menu, HOST LOBBY creates a discoverable Steam room and JOIN LOBBY opens the in-game room list. The list shows the host, player count and installed-version compatibility before joining.

Version 0.8.3 added the optional Isaac-style three-player HUD. Version 0.8.2 added shared run seeds, layout fingerprints and safe floor-load fallbacks.

Version 0.8.1 fixes the black/over-zoomed client view during floor transitions by parking persistent remote players beside the local player until the synchronized dungeon is ready, and retries room placement when generation finishes late.

Version 0.8.0 replaces visual-only remote sprites with network-controlled real PlayerController instances. Remote players now participate in the built-in co-op camera, collision, room, enemy targeting, inventory and floor-transition systems. It also fixes the lobby player-list construction error, makes the connection handshake idempotent and removes per-second packet-poll log spam. Version 0.6 added persistent remote players across scene changes, smoother 20 Hz player snapshots, stable host-driven floor transitions, exact modded pickup identity matching, and safer gameplay patches. Version 0.5 added host-authoritative enemy projectiles, exact projectile matching for multi-shot/charged guns, beam synchronization, and a locked run roster. New players may join in the foyer; after the run starts, only a disconnected member of that run may reconnect.

[!WARNING] THIS MOD IS STILL VERY EARLY IN DEVELOPMENT - DO NOT EXPECT A FUNCTIONAL EXPERIENCE RIGHT NOW

WIP WIP WIP WIP WIP WIP pls be nice

[!WARNING] ON HOLD, HAD SOME HUGE UNEXPECTED LIFE THINGS GET IN THE WAY, DO NOT WORRY, THIS MOD IS STILL IN DEVELOPMENT AND WE ARE STILL EXTREMELY EXCITED ABOUT THE FUTURE OF GUNGEONTOGETHER

The mod is free (because I'm not weird). however I'm broke asf so feel free to donate for my INSANELY INTENSE AND HARD LABOUR (jk) My paypal is [email protected] if you actually want to (for some reason)

Contributers

[!NOTE] As this mod runs through the steam network, it only works with the steam verison of the game as steamID is required

Features

What works so far

System	Status	Notes
Steam invites/lobby system	🟩 Done	Steam lobby creation and joining functional
Steam P2P networking	🟨 Working	Real connections and Steam invites working
Three-player HUD	🟨 Working	Isaac-style corner HUD; F8 switches to the native HUD
Player Synchronization	🟨 Working	Real remote PlayerControllers with 20 Hz movement and animation sync
Three-player co-op	🟨 Working	Native co-op room rules, three-player bounds camera and real PlayerControllers
Enemy Synchronization	🟨 Working	Host-driven enemies across active rooms, including state and projectiles
Weapon Synchronization	🟨 Working	Projectiles/beams plus full gun inventory, selection and per-gun ammo snapshots
Reconnection	🟨 Working	Run roster locks after leaving the foyer; prior members can reconnect
Dungeon Synchronization	🟨 Working	Shared seed, layout fingerprint and safe mismatch rejection
Items/economy	🟨 Working	Full passive/active inventory snapshots, host-authoritative ground pickups, shared keys and money
Down/revive	🟨 Working	Nearby living teammate revives a downed player after three seconds
Singleplayer	🏁 Finished	Yippeeee!!!!!

Planed for 1.0 release

• Online co-op multiplayer for Enter the Gungeon
• Steam P2P networking (no dedicated servers required), no parsec or streaming required
• Real-time synchronisation of
  • Players
  • Enemies
  • Projectiles
  • Dungeon
• Debug controls for testing
• Spectate when dead
• Enemy scaling (set difficulty in game)

Planned for the future

• EPIC GAMES SUPPORT (EOS P2P)
• Unlimited players
• EVERYTHING synced
• Custom Game Modes
  • Race mode (competing in identical dungeons, first player to finish wins)
  • Mirror mode (identical dungeons, can hurt one another but can't see eachother, shooting is synced across dungeons)
• Teammate revive items
• Team based buffs and items

Installation

1. Install BepInEx for Enter the Gungeon
2. Copy GungeonTogether.dll to [ETG Install]/BepInEx/plugins/
3. Launch Enter the Gungeon

Building

This only applies to people who want to build from source, or if we forget to post builds :)

1. You will need to setup BepInExPack_ETG (either with a mod manager like r2ModMan or manually)
2. Place the required game, BepInEx and ModTheGungeon reference assemblies in GungeonTogether/Libs/
3. Run dotnet build GungeonTogether/GungeonTogether.csproj -c Release
4. Launch Enter the Gungeon

Technical Details

Built with BepInEx framework using Steam P2P networking for a seamless multiplayer experience. Unfortunately if you play the game through epic or windows store this mod will not work, as it runs through steams p2p api only, which means you need a steamID for it to work. Sorry guys... (EPIC COMING SOON)

[!NOTE] Wiki!!! https://deepwiki.com/llamerrr/GungeonTogether Thanks to https://github.com/TheExploration

1.0 release coming one day!!!!!!