Two cheat mods in a weekend: Mono vs IL2CPP and eight places where Unity modding breaks

The author shares their experience developing cheat mods for Unity-based games, comparing the Mono and IL2CPP architectures. While creating mods for Valheim and a Go Next! demo, the author identified significant differences in modification approaches. The article highlights eight critical pain points, ranging from BadImageFormatException errors when using MelonLoader to challenges with interop, lost GUILayout functionality, and input handling issues. The author explains why automated solutions often fail and why manual code patching is more reliable than standard methods like PlayerPrefs or SetGodMode. This article serves as a practical guide for mod developers facing Unity's limitations when transitioning from the traditional Mono environment to the optimized IL2CPP, offering solutions for common errors and strategies for injecting custom code into compiled game builds.