FMassEntityManager supplies API for entity creation (that can result in archetype creation) and entity manipulation. Even though synchronized manipulation methods are available in most cases the entity operations are performed via a command buffer. The default command buffer can be obtained with a Defer() call. FMassEntityManager are meant to be stored with a TSharedPtr or TSharedRef. Some of Mass API pass around FMassEntityManager& but programmers can always use AsShared() call to obtain a shared ref for a given manager instance (as supplied by deriving from TSharedFromThis). IMPORTANT: if you create your own FMassEntityManager instance remember to call Initialize() before using it.