Alright, I realize that this isn't the first puzzle I've posted here. But this is the first one with a number attached.
Anyway, I'm planning to post a series of progressively more difficult puzzles across similar themes, about one per week.
Because the puzzles will get rather difficult eventually, I will post one hint per day.
I'm going to start off with a simple what's missing:
Contraband
Workshop
Mountebank
Festival
Tournament
Gold
King's Court
Swindler
Embargo
Saboteur
Lookout
Torturer
Caravan
Trade Route
Outpost
Hint 1: Honorable mention goes to Envoy, Stash, and Province
Hint 2: This is based on card text, not mechanics.
Hint 3: It might be a good idea to look at all of the cards from, say, Prosperity, by themselves.