Rules question: With Black Market, can only 1 Castle be in the deck? And how do you choose which one?
Same question for the split piles, can you have either of the cards in the BM deck, and how would you choose it?
I believe Donald's ruling for this so far has been: do what you want. Which is a fine ruling, I think.
What I envision Black Market doing is creating a Black Market supply. For each card in the Black Market deck, there is a pile in the Black Market supply that is set up just as it would have been in the real supply. So, for example, if Castles were in the Black Market supply, Humble Castle would be on top just like in the real supply. Since each pile in the Black Market supply can be accessed only once, the top card (Humble Castle) is the only one that can ever be purchased.
Of course, that's just my logic for figuring out how I would want to handle this in my IRL games. Until this question is answered by the online version, I guess anything goes.