MelonLoader is a universal mod loader designed for Unity games on Windows. It supports both major Unity scripting backends: Mono and Il2Cpp. While installing mods as a user is mostly the same for both backends, the technical requirements and mod compatibility rules are different. Understanding these differences is essential to avoid crashes, errors, or non working mods.
Understanding Unity Backends: Mono vs Il2Cpp
The scripting backend determines how a Unity game runs its C# code. This directly affects how mods interact with the game.
Mono Backend Explained
Mono uses just in time compilation. The game’s C# code is compiled while the game is running.
Key characteristics of Mono games:
- Game logic is stored in readable C# files such as Assembly-CSharp.dll
- Easier access for mod developers
- Mods are generally simpler to create
- Slightly lower performance compared to Il2Cpp
Il2Cpp Backend Explained
Il2Cpp uses ahead of time compilation. The game’s C# code is converted into C++ and then compiled into native machine code before release.
Key characteristics of Il2Cpp games:
- Game logic is compiled into GameAssembly.dll
- Original C# code is not directly readable
- Modding requires generated proxy assemblies
- Higher performance but increased modding complexity
Because of this difference, Mono mods and Il2Cpp mods are not interchangeable.
Step 1: Installing MelonLoader for Mono and Il2Cpp Games
The MelonLoader installation process is mostly universal, but Il2Cpp games require additional dependencies.
Required Dependencies
For Mono Games
- Microsoft Visual C++ Redistributable (matching x64 or x86 game architecture)
- .NET Desktop Runtime is not strictly required by MelonLoader itself
For Il2Cpp Games
- Microsoft Visual C++ Redistributable (matching x64 or x86 game architecture)
- .NET Desktop Runtime 6.0 or newer is required and mandatory
Missing the .NET runtime is the most common reason MelonLoader fails on Il2Cpp games.
Installing MelonLoader Using the Automated Installer
- Download the official MelonLoader installer from
https://melonloader.pro/download-melonloader/ - Run the installer as administrator
- Click Select and browse to the game executable file
Example: GameName.exe - Leave the MelonLoader version set to the latest stable release unless a mod requires a specific version
- Click Install
- Launch the game once after installation
On first launch, MelonLoader creates these folders inside the game directory:
- MelonLoader
- Mods
- Plugins
- UserData
A console window appearing during startup confirms successful installation.
Step 2: Installing Mods for Mono and Il2Cpp Games
From a user perspective, mod installation is the same for both backends. The difference lies in which mods you are allowed to use.
Important Compatibility Rule
You must always use mods that match your game’s backend:
- Mono game requires Mono compatible mods
- Il2Cpp game requires Il2Cpp compatible mods
Using a Mono mod in an Il2Cpp game will not work and often causes errors.
Mod Installation Steps
- Download the mod file, usually a .dll
- Place mod .dll files into the Mods folder
- Place plugin .dll files into the Plugins folder
- Launch the game
The MelonLoader console will display whether each mod loaded successfully.
Configuration files such as .cfg or .json are usually created automatically inside the UserData folder after the first run.
Step 3: Why Il2Cpp Mods Are Different (Developer Explanation)
While users only need to place mod files correctly, Il2Cpp introduces complexity for mod developers.
How Mono Mods Access Game Code
- Mods directly reference Assembly-CSharp.dll
- Game logic is fully readable C#
- MelonLoader loads and executes mod code directly
How Il2Cpp Mods Access Game Code
- Original C# code is compiled into native C++
- MelonLoader automatically generates proxy assemblies on first launch
- These generated files are stored in the MelonLoader Managed folder
- Developers reference these generated assemblies when creating mods
These generated assemblies are often called unhollowed assemblies. They contain class names and method signatures but not full original logic. This is why Il2Cpp mods must be built specifically for Il2Cpp games.
Common Mistakes to Avoid
- Installing Mono mods in Il2Cpp games
- Skipping .NET Desktop Runtime installation for Il2Cpp
- Using outdated mods after a game update
- Running the installer without administrator permissions
- Allowing antivirus software to delete version.dll
Quick Compatibility Checklist
Mono Game
- MelonLoader installed
- Visual C++ Redistributable installed
- Mono compatible mods only
Il2Cpp Game
- MelonLoader installed
- Visual C++ Redistributable installed
- .NET Desktop Runtime 6.0 or newer installed
- Il2Cpp compatible mods only
Final Summary
MelonLoader supports both Mono and Il2Cpp Unity games, but mod compatibility depends entirely on the game’s scripting backend. Installing MelonLoader is nearly identical for both, but Il2Cpp games require additional runtime dependencies and backend specific mods. As long as the correct prerequisites are installed and the correct mod type is used, MelonLoader works reliably on both backends.
Official MelonLoader installer:
https://melonloader.pro/download-melonloader/
GitHub releases: https://github.com/LavaGang/MelonLoader/releases