Foreign Market
Always good to make reference to official cards when doing the wording and formatting.
I think this will be a lot of fun in games where it's the only +buy - you get the first use of it and a Coffers, but then other players get the benefit of the +buy when you might really want it. Might be my favourite version of the rotating card that I've seen on this forum in terms of how I imagine games with it. Well done.
Pastor
Great idea, but I think it might just be a bit too hard to make this go crazy. Even getting it to gain a $3 will be work and you can only do so much trashing without something like Trail or Fortress. Without it you'd need a deck drawing engine and another trasher, which you aren't using to its full extent early on, before you can use this to have a megaturn. Would be worth playtesting but I think if you pursue the megaturn strategy with this on boards with the right pieces, you'll lose to a generic engine strategy. So in most games I think it will just be a cantrip trasher. That's not so bad (I often buy Priest without making use of the when trash +$2), but I think the card would be better if it was a little stronger, like if the card was gained to your hand (encouraging even Copper gaining).
Old Uni
I like the effects choices of this card, though the third might be a bit time consuming and the card would be fine without it. It having a potion cost I think lets it down in comparison to University, and it would be fine at $5.
Young Pirate
The kind of card I had in mind when I called this contest. It's got the same mechanic as Pirate, but because it doesn't gain a treasure, it highlights some of Pirate's other interactions. I don't really like the combination of cards and $. $ is great because it makes you think about balancing treasure and non treasure payloads. If I was designing it I would have made it "Now or at the start of your next turn, +$2, +1 buy" for $4. But seems fun.
Lord
I like this better than Nobles and Harem. It makes the midgame more interesting. Peddler Variants are often a "why not" card more than something necessary (the only +actions) or regrettable (a Silver), so finally you have to think early about the opportunity cost of only getting a Peddler for $6 for the VP advantage. Not the most inspiring card but this would have been great in Intrigue 2E to replace Harem.
Night Shift
A nice extra turn card to add to the collection. Maybe a bit too Big Money incentivising.
Commander
This will be mostly used to play other $5 cards (assuming you round down) and $2 cards, not the $3 and $4 cards BOM tends to play. So a great complement. I think a $5 card that gives a debt is a $3 card (I entered it in a competition) so strength-wise it's about right. The more I think about this card, the more I like it.
Yeoman
The closest comparison I can see is Wheelwright, which has the same interactions but stronger. You would at least want the Silver gaining (and maybe all gaining) to be to your hand for a $5 card. If that's what you meant to do, then this is a nice explorer replacement with some extra utility in the late game with spare + actions. But I have to judge what I see.
Gilded City Guardian
Probably about right strength wise and it would be decently fun online. Donald X didn't do non terminal Boon cards for a reason. Also with this card it would be easy in multiplayer to limit the availability of Boons by setting aside a bunch.
I don't really like Hexes or Cursed Village which is clouding my judgement of the heirloom, but it isn't really a good complement to the main card in my view.
Loyal Village
The difference with Underling is you'd buy this even if you weren't all that interested in the Ally. So it's a nice introduction to the mechanic, as well as +action management which I like. Good, simple card.
Redoubt
A great Dark Ages card. Has a pile emptying interaction with Watchtower. But I like this better than Fortress as you can imagine the Draw to X and trashing coming into play in the same games (as trashing benefits small hands). Good card.
Porticulis
Great intention, just a little too strong even at $4. Exploration is a decent buy that often only gives you +1 Coffers and +1 Villager once. Even just the Villager and you have an excellent card that would be bought in a lot of games.
Sepulcher
I imagine the fun of a someone else Knight or Bandit trashing a one of your Golds, triggering this reaction, and gaining the last province to win the game. EDIT: This imagination caused me to pay less attention to the actual card text, which specifies non victory. In fact I imagine a lot of fun interactions with this card. Great design.
Herder
As an aside, if I was allowed to enter I'd do some sort of Crypt or Archive variant, so you hit a nerve for me with this one. This is the kind of card where I'd like to see a top ranked player make an engine when it's the only +Actions card. You probably want it as a pseudo trasher/exiler, but making the most of it is a different matter. An engine enabled by early greening - what a concept! What a delightful card.
Adventurer
Treasure Trove is one of my favourite cards, but this is a bit too strong. Treasure Trove being a Treasure still encourages you to play around a bit with Terminal Draw and other enablers. Can't imagine doing anything but playing BM with this card.
Guild Warehouse
I like your intention here. The strongest aspect of this card is the combination of sifting and +buy. It is an invitation for early greening. But I'm not sure it really stands out as a $5, though I agree with what you're saying about how beginners see Market (It's how I saw it).
Distributor
It will come down to the cards in the pile. Gaining the card after choosing to rotate is a good way to prevent spiteful play. It will suck to miss out on a card (though it moves slowly enough that you can't blame other players).
Poltergeist
Making more accessible versions of powerful cards is a great idea. The best comparison for this card is Scavenger - instead of +$2, you get +1 Card and +1 Action at the start of your next turn, and it's non terminal. I don't think it needs to be gained to hand - it's powerful enough without it and compares too favourably to Ghost Town with it.
Unnamed Way of the Turtle inspired card
The Way of the Turtle and Voyage interaction is a great one (especially with multiple turns) so good on you for trying to recreate a fun interaction in a single card. It's not clear from the wording whether you get the effect of the action on play, or whether it's a compulsory Way of the Turtle. The former is way too powerful - an extra turn being even more powerful than your first one. The latter means basically you get to tee up 1 card for your next turn, and buy whatever your treasures can afford, which isn't all that interesting. Something like a +1 Action, unbounded Royal Galley might be what you're after. Also there's nothing in the rules saying what a "terminal" is.
Story
What you've shown me is that being a Treasure makes Black Market much cleaner. This fits the contest brief nicely - more Black Market, this time with events. I can foresee a few tracking issues, but it would be a fun online card. I have concerns that events can be more influential from a single buy than cards. Hitting Inheritance or Lost Arts can give your deck an immense advantage that would be hard to replicate with a single copy of a card.
Hidden City Explorer
High risk, high reward. The card is a terrible $5 but the hidden cities are outstanding and could turn the tide of the game. I think there's a bit too much luck involved to get a Hidden City, with what your "secret" card is in the opening, and with getting first access to the Hidden City that will win you the game (which might depend more on the kingdom than how the game is played).
Indulgence
Another entry that is a cleaner version of an existing mechanic. Not as high stakes as Mining Village, where making the wrong decision on when to trash that card can end up making your deck not function. This is a lower risk card, especially if you end up with an abundance of +buys, so it's a nice exploration of what Mining Village has to offer that encourages actually using the trashing function more aggressively. A good entry.
Trust Fund
Initially I thought this was way too weak, then I realised that you would want to put a variety of Victory cards on it. There's a clear strategy here - set aside an estate and a province, and pick +1 Card +1 Action, and you can green without hurting your engine. Kind of like Sanctuary. I'd like to see how Duchies and Alt VP come into it. But what you end up with is a very different game of Dominion with a different flow. A very game warping landscape (like Keep) - and I'm not sure whether I'd have more fun in games using it.
Rat King
City Quarter is better than this except for the remote possibility of dishing out a Hex. This can have a much lower cost and avoid hexing. The card this makes me think of is Crossroads - turning "junk" into draw, but with a specific kind of junk. Could be fun to play with at a lower cost.
Oil Merchant
+$3, +1 Buy with a compulsory Borrow - probably too strong for $5 as a BM card. That's without the Action opt out. For much of the game you're buying Actions with this (if you're making an engine) so it's very strong. Probably too strong and will lead to games that are over too quickly.
Outcast
One of the other contests I won used a similar concept (Loner, contest #54). So clearly I like the premise. But this card is too strong. It's way too much of a no brainer to buy at least one, which is at no risk of leaving your deck. The others are nice bonuses, and I don't think it's too hard to get past the point where you're likely to net more than $3 value from playing Outcast and be able to buy it back.
__________________________
This was a very hard contest to judge. Many cards perfectly fit the brief and I can't suggest any improvements. Many would fit very nicely into next editions of the original card's sets. Overall I hope you had fun thinking about your favourite cards.
There can only be one winner, and that is
Commander, by Udzu
Runners up: Herder by faust and Sepulcher by Gubump