Marching Orders prevents players from marshaling locations or attachments as duplicates.
- Marching Orders does not prevent marshaling cards into shadows, nor bringing locations and attachments out of shadows. It does however prevent playing events from shadows. (Source)
You can marshal duplicates, because the card did not state otherwise. — Madnico 1
"Marshal a duplicate" is not a distinct player action. You initiate a "marshal a character/location/attachment" player action, and the card enters play as a duplicate. And while Marching Order is revealed, you cannot initiate the "marshal a location/attachment" player action. See the ruling on Arbor and duplicates, also the ruling on Barring the Gates. — mplain 213
A player with Marching Orders revealed can marshal locations, attachments, and events into shadows, and bring locations and attachments out of shadows. They cannot play the event from shadows, however. — scantrell24 3263