UnityEngine.GameObject not marked as Serializable?

The serialization is an effort to do a deep copy using binary formatter and memory stream. It works perfect if the item I'm deep copying doesn't contain a reference to a GameObject. When it does, it throws the error that the GameObject is not marked as serializable.

Unity doesn't use the C# serializer. They uses their own serialization method. $$anonymous$$ost UnityEngine classes have a counterpart in native code. They are more than the managed representation you can see from $$anonymous$$ono. Don't mess around with lowlevel stuff when it comes to build in classes of Unity.

They actually sealed all classes so you don't accidentally derive a class from a Unity class. The only classes that can and should be used as base class is $$anonymous$$onoBehaviour and ScriptableObject (and the editor classes that are ment to be derived like Editor, EditorWindow, AssetPostprocessor, ...)

If you want to deep copy a UnityEngine.Object derived object, use Instantiate. It works with most objects (i used it already for $$anonymous$$aterials, $$anonymous$$eshes and of course gameobject and components). $$anonymous$$eep in mind when you clone a component the owning gameobject is cloned as well along with all components and child objects.