Can the person who has the knife really just order the dark one to do what they say…no idea how much the original dark one was telling the truth about the knife.
Yes, I think they can. The guard ordered the original dark one around like that and when Rumpel called Zoso he acknowledged that Rumpel could now control him. He could have been playing a part but I think he was telling the truth about the dagger.
It would be a VERY useful thing for Regina to get her hands on. She wouldn’t kill him with it though, unless she doesn’t KNOW that it would make her like him! Hmm. Rumpel might succeed in keeping that from her and trick her to use it. Which would be quite a good revenge on someone as vain as her.
But I do not believe that she knows about it. And I think that he does have it protected somewhere.