npx skills add ...
npx skills add reason-machines/devtools-skills --skill subnautica-2-deep-synergy-coop-mod
BepInEx-based cooperative multiplayer mod for Subnautica 2 with synchronized sessions, shared inventory, and AI-enhanced narrative generation
npx skills add reason-machines/devtools-skills --skill subnautica-2-deep-synergy-coop-mod
Skill by ara.so — Devtools Skills collection.
Deep Synergy is a BepInEx-based cooperative multiplayer modification for Subnautica 2 that transforms the single-player survival experience into a synchronized multi-player session. The mod implements deterministic session synchronization (DSS), adaptive dynamic scaling (ADS), and decentralized peer-to-peer networking to enable seamless co-op gameplay without central server infrastructure.
Key Capabilities:
Install BepInEx 6.0.x for Subnautica 2:
Download Deep Synergy Mod:
<game_root>/BepInEx/plugins/Expected log output:
BepInEx/config/synergy_profile.json)Key Configuration Fields:
difficulty_scale: "static", "adaptive", or "linear" - controls how game difficulty adjusts with player countresource_multiplier: Float multiplier for harvestable resource nodes (1.0 = vanilla, 2.0 = double)oxygen_consumption: Fraction of normal oxygen drain (0.5 = half drain, 1.0 = vanilla)creature_spawn_divider: Reduces creature spawns (2.0 = half spawns)time_of_day_sync: "host" (host controls time), "all" (synced vote), "independent" (client-specific)api_key_env: Environment variable name containing API keys (never hardcode keys)BepInEx/config/session_config.xml)Access the BepInEx console with F12 (default binding, configurable):
The mod uses BepInEx IL2CPP hooking. To extend functionality:
Console workflow:
Generate narratives during gameplay:
Cause: NAT traversal failed or host disconnected
Solution:
Cause: High latency or packet loss causing Merkle tree mismatch
Solution:
Cause: IL2CPP hook failure or incorrect installation
Solution:
BepInEx/LogOutput.log for errors.dll files are in BepInEx/plugins/BepInEx/cache/ and restart gameCause: Missing or invalid API keys
Solution:
Check config references correct env var:
Cause: Network congestion or inefficient sync intervals
Solution:
Cause: Creature AI state lattice desync
Solution:
Edit synergy_profile.json to add biome-specific resource scaling:
Enable session save/load:
Load saved session:
Add custom translations in BepInEx/config/localizations/custom_en.json:
Reference in code:
[Info : BepInEx] BepInEx 6.0.0 - Subnautica2 (5/14/2026)
[Info :DeepSynergy] Deep Synergy Multiplayer Mod v1.0.0 loaded
[Info :DeepSynergy] Session Manager initialized
[Info :DeepSynergy] WebRTC transport layer ready{
"session_name": "Deep Exploration Team",
"max_players": 4,
"difficulty_scale": "adaptive",
"resource_multiplier": 1.5,
"oxygen_consumption": 0.85,
"creature_spawn_divider": 1.5,
"enable_pvp": false,
"friendly_fire": false,
"shared_blueprints": true,
"ping_locations_shared": true,
"time_of_day_sync": "host",
"voice_chat_integration": "discord_rpc",
"locale": "en_US",
"api_integration": {
"openai": {
"enabled": false,
"api_key_env": "OPENAI_API_KEY",
"model": "gpt-4",
"role": "narrator"
},
"claude": {
"enabled": false,
"api_key_env": "ANTHROPIC_API_KEY",
"model": "claude-3-opus-20240229",
"role": "lore_engine"
}
},
"network": {
"nat_traversal": true,
"max_latency_ms": 250,
"sync_interval_ms": 50,
"inventory_hash_algorithm": "sha256"
}
}<?xml version="1.0" encoding="utf-8"?>
<SynergyConfig>
<Session>
<DefaultPort>25565</DefaultPort>
<EnableUPnP>true</EnableUPnP>
<MaxConnectionAttempts>5</MaxConnectionAttempts>
<ConnectionTimeoutSeconds>30</ConnectionTimeoutSeconds>
</Session>
<Synchronization>
<InventoryHashInterval>1000</InventoryHashInterval>
<CreatureStateInterval>200</CreatureStateInterval>
<BaseStructureInterval>500</BaseStructureInterval>
</Synchronization>
<Logging>
<Level>Info</Level>
<EnableNetworkDebug>false</EnableNetworkDebug>
</Logging>
</SynergyConfig># Start hosting a session
/start_server
# Output: Server created: session code = 9B2A-4C7D-E8F1
# Join existing session
/join_session 9B2A-4C7D-E8F1
# Check connection status
/synergy_status
# Output:
# Connected peers: 3/4
# State sync: 100% complete
# Inventory hash: 0xFA342B1E
# Avg latency: 45ms
# Leave session gracefully
/disconnect_session# Temporarily adjust difficulty multiplier
/synergy_scale 1.5
# Reset to config defaults
/synergy_reset
# Force world seed sync (host only)
/seed_override 8251# Trigger OpenAI narrative generation
/api_narrate "discovered alien artifact in lost river"
# Generate species biology log with Claude
/api_lore_generate "ghost leviathan juvenile"
# Show last 5 AI-generated journal entries
/api_journal_history 5# Enable verbose network logging
/debug_network true
# Dump current inventory Merkle tree
/debug_inventory_tree
# Force state resync
/force_resync
# Show desync detection results
/debug_conflictsusing BepInEx;
using BepInEx.IL2CPP;
using HarmonyLib;
using DeepSynergy.Core;
namespace DeepSynergy.CustomExtension
{
[BepInPlugin(PluginGUID, PluginName, PluginVersion)]
[BepInDependency("com.deepsynergy.core")]
public class CustomExtensionPlugin : BasePlugin
{
public const string PluginGUID = "com.yourname.customextension";
public const string PluginName = "Custom Deep Synergy Extension";
public const string PluginVersion = "1.0.0";
private Harmony _harmony;
public override void Load()
{
_harmony = new Harmony(PluginGUID);
_harmony.PatchAll();
// Hook into session events
SessionManager.OnPlayerJoined += OnPlayerJoinedHandler;
SessionManager.OnInventorySynced += OnInventorySyncedHandler;
Log.LogInfo($"{PluginName} loaded successfully");
}
private void OnPlayerJoinedHandler(string playerId)
{
Log.LogInfo($"Player joined: {playerId}");
// Custom logic here
}
private void OnInventorySyncedHandler(InventorySyncData data)
{
Log.LogInfo($"Inventory synced - hash: {data.MerkleRootHash}");
}
}
}using HarmonyLib;
using DeepSynergy.Core;
namespace DeepSynergy.CustomExtension
{
[HarmonyPatch(typeof(Player), "ConsumeOxygen")]
public static class OxygenConsumptionPatch
{
static void Prefix(ref float amount)
{
// Apply session multiplier from config
float multiplier = SynergyConfig.Current.OxygenConsumption;
amount *= multiplier;
// Sync to other clients
if (SessionManager.IsHost)
{
NetworkSync.BroadcastOxygenEvent(amount);
}
}
}
}using DeepSynergy.API;
using System.Threading.Tasks;
public class CustomNarrativeGenerator
{
private readonly OpenAIClient _openai;
public CustomNarrativeGenerator()
{
string apiKey = Environment.GetEnvironmentVariable("OPENAI_API_KEY");
_openai = new OpenAIClient(apiKey);
}
public async Task<string> GenerateBaseDescription(BaseStructure baseData)
{
string prompt = $@"Generate a brief narrative description for an underwater base:
- Location: {baseData.Biome}
- Depth: {baseData.DepthMeters}m
- Components: {string.Join(", ", baseData.Modules)}
- Players: {baseData.PlayerCount}
Keep it under 100 words, immersive tone.";
var response = await _openai.GenerateCompletion(prompt, maxTokens: 150);
return response.Text;
}
}{
"session_name": "Resource Run",
"max_players": 2,
"difficulty_scale": "static",
"resource_multiplier": 1.3,
"oxygen_consumption": 0.9,
"creature_spawn_divider": 1.2,
"shared_blueprints": true,
"time_of_day_sync": "host"
}# Player 1 (Host)
/start_server
# Share code 4A7B-9C2D-E5F3 with Player 2
# Player 2 (Client)
/join_session 4A7B-9C2D-E5F3
# Both players check sync
/synergy_status{
"session_name": "Mega Base Construction",
"max_players": 4,
"difficulty_scale": "adaptive",
"resource_multiplier": 2.0,
"oxygen_consumption": 0.7,
"creature_spawn_divider": 2.0,
"shared_blueprints": true,
"ping_locations_shared": true,
"time_of_day_sync": "all"
}{
"session_name": "Lore Expedition",
"max_players": 2,
"api_integration": {
"openai": {
"enabled": true,
"api_key_env": "OPENAI_API_KEY",
"model": "gpt-4",
"role": "narrator"
},
"claude": {
"enabled": true,
"api_key_env": "ANTHROPIC_API_KEY",
"model": "claude-3-opus-20240229",
"role": "lore_engine"
}
}
}/api_narrate "entering the blood kelp zone at 300m depth"
# Output: "The crimson fronds pulse with bioluminescent life as the team descends..."
/api_lore_generate "crabsquid behavior patterns"
# Output: "Species: Crabsquid (Elektrus Crustacea)..."# Check NAT configuration
/debug_network true
# Look for "NAT type: Symmetric" in logs (problematic)
# Enable UPnP in session_config.xml
<EnableUPnP>true</EnableUPnP>
# Alternative: Port forward 25565 on router# Check current sync status
/debug_conflicts
# Force full resync
/force_resync
# Adjust sync interval in config
"sync_interval_ms": 100 # Increase from 50ms# Verify environment variable is set
# Windows PowerShell
echo $env:OPENAI_API_KEY
# Linux/macOS
echo $OPENAI_API_KEY
# Set if missing (do NOT commit to code)
# Windows
setx OPENAI_API_KEY "your-key-here"
# Linux/macOS
export OPENAI_API_KEY="your-key-here""api_integration": {
"openai": {
"api_key_env": "OPENAI_API_KEY" // Must match env var name
}
}# Check current latency
/synergy_status
# If avg latency > 150ms, adjust config
# Increase sync intervals in session_config.xml
<InventoryHashInterval>2000</InventoryHashInterval> # From 1000
<CreatureStateInterval>400</CreatureStateInterval> # From 200
# Reduce max players
"max_players": 2 # From 4# Enable creature debug logging
/debug_network true
# Check creature sync interval
<CreatureStateInterval>200</CreatureStateInterval>
# Force creature state resync (host only)
/force_resync creatures{
"biome_overrides": {
"safe_shallows": {
"resource_multiplier": 1.0,
"creature_spawn_divider": 1.0
},
"kelp_forest": {
"resource_multiplier": 1.2,
"creature_spawn_divider": 1.3
},
"blood_kelp_zone": {
"resource_multiplier": 1.5,
"creature_spawn_divider": 2.0
},
"lost_river": {
"resource_multiplier": 2.0,
"creature_spawn_divider": 2.5
}
}
}{
"session_persistence": {
"enabled": true,
"autosave_interval_minutes": 10,
"save_directory": "BepInEx/saves/",
"compress_saves": true
}
}/load_session "Deep_Exploration_2026-05-14"{
"ui.session.created": "Session established: {0}",
"ui.player.joined": "{0} has entered the abyss",
"ui.inventory.synced": "Inventory synchronized",
"console.help.start_server": "Create a new multiplayer session"
}string message = LocalizationManager.Get("ui.player.joined", playerName);{
"network": {
"compression": "lz4",
"delta_encoding": true,
"sync_radius_meters": 500, // Only sync entities within 500m
"inventory_batch_updates": true
}
}{
"performance": {
"reduce_sync_precision": true, // Reduce float precision for position sync
"skip_inactive_entities": true, // Don't sync entities outside render distance
"lazy_merkle_updates": true // Update inventory tree only on change
}
}