I'm making a migration tool for scene's and am now including prefabs and nested prefabs. To migrate the data I need to know what type of class/MonoBehaviour the document is (can be found with the original fileID and guid). For a normal prefab (without the nesting) this can be done by going in the scene file to the PrefabInstance -> M_Modification -> M_Modifications -> Target -> fileID This fileID then is the flag of the document in the prefab file i'm working with (a quick ctrl + f shows what script it is). But this does not seem to work when prefabs are nested. It then has a fileID that does not exist anywhere else in the project (that i can find). It seems just randomly generated like the normal prefab and a reference to something i can't find as it changes when the script is re-added. I've exported it to a package and unzipped it but there isn't any special mapping other then the normal files. But the import in a new project works fine, which should mean that the fileID is some kind of a reference as the reference stays intact. (I've added the package to the post) Any information about the nested prefab fileID would be appreciated.