Mono and IL2CPPA Unity-developed scripting back-end which you can use as an alternative to Mono when building projects for some platforms. More info
See in Glossary internally cache all C# reflection (System.Reflection) objects and by design, Unity doesn’t garbage collect them. The result of this behavior is that the garbage collector continuously scans the cached C# reflection objects during the lifetime of your application, which causes unnecessary and potentially significant garbage collector overhead.
To minimize the garbage collector overhead, avoid methods such as Assembly.GetTypes and Type.GetMethods() in your application, which create a lot of C# reflection objects at runtime. Instead, you should scan assemblies in the Unity Editor for the required data and serialize and/or codegen it for use at runtime.