I'll do short comments on al cards.
I like the concept of a reserve hand. It is not entirely new as a concept - Native Village kind of did that - but having multiple cards interact with the same set aside cards is interesting. I agree you should probably pick a different name.
1.
Army
5
Action- Attack
+2$. Each other player discards down to three cards in both their hand and reserve hand.*
This is probably fine. One complaint is that in absence of other reserve hand interactions, it's just an expensive Militia (and I guess if you're starting with 4 cards in your reserve hand, it even gives a free Silver on the first play). That's a bit boring; you could probably go for a effect that is a bit stronger on a $5 (may you have the player gain junk to their reserve hand?). Conceptually, it may be a bit problematic have a card that discourages using the reserve hand cards, because that is the main focus of the expansion.
2.
Blacksmith
6
Action
+5 cards. Discard 1 card per action you have.
Could be a bit nasty on BM. Generally, you should be able to play this with 1 action left, so most of the time it's +5 cards, discard 1, which compares a bit too well to Hunting Grounds I think. I like the idea, but it may be hard to balance.
3.
Carrier Pigeon
2
Action-Reaction
+2 cards. Discard a card from your reserve hand.
When another player plays an attack, you may first reveal this to exchange your hand for your reserve hand
This is just really bad without attacks. You start with mostly junk in your reserve hand, so you don't want to discard it all. With attacks... I'm just not sure how good it is? You could save a good hand if you'd have to discard, but then your good cards are hidden away and you depend on the other player to give them back to you. Overall, I think this is pretty weak, but there could be boards where you want it.
4.
Dining Hall
5
Action
Dining Hall: +3 cards +1 action. Put 2 cards from your hand into your reserve. Discard 2 cards from the reserve.
It's a fancier Forum; draw 3, discard two, but you can store the junk away a bit longer. Seems fairly balanced, but not too exciting.
5.
Divine Light
4
Action
+1 Card. +1 Action. Set this on your Tavern Mat. At the start of your turn you may call this to discard your hand, your reserve hand or both. If you discard a hand, +5 cards to that hand.
It should probably be "if you discarded at least 1 card that way, do X". This is also a fancier version of Guide. I think I would like it better if the on-play effect was more different from Guide. Discarding your reserve hand only does something the first time, so this ability is kind of a 1-shot unless there are other cards that put things to your reserve hand. But as a 1-shot, it's pretty good and unique, so I think it works out.
6.
Foreign Market
5
Action
+ 1 Card. +1 Action. +1 Coin. Discard any number of cards. +1 Buy per card Discarded.
The card seems okay. Mostly not too interesting probably. However you can easily empty the Curse pile with this/Watchtower, so there's at least one fun interaction.
7.
Fork in the Road
2
Action
+1 Action. When you would draw a card this turn you may draw it to your reserve hand. +1 Card.
I suggest adding a "While this is in play" clause instead of putting it directly there. You need to clarify if you have to decide where to draw it before or after you see the card. I assume before (the other option is way too strong). That makes the card just a super-weak Native Village that cannot get back its cards. Sometimes, you can control that you have a green card on top of your deck, but I don't see many other uses for this.
8.
Godly Thunderbolt
2
Action
You may trash this and your hand if you did +5 cards +1 Action
This is amazingly strong and probably better than Chapel, but also swingier - if you open this/some terminal, colliding them is super bad, not colliding them is super awesome. I don't like it.
9.
Lost purse
3
Treasure
0$. While this is in play you may play treasures from your reserve hand.
I don't think this works without other reserve hand cards. May add a "when you discard this from play, gain a Silver to your reserve hand" or something?
10.
Mosque
2
Action
Trash up to 5 cards from your reserve hand
This is completely useless without other reserve hand interactions. Even with them, I don't think there are many cards (at least so far) that would make this a decent buy.
11.
Museum Collection
6
Reaction-Victory
Worth 1 VP per 3 cards in your reserve hand at the end of the game. Reaction when you would exchange your hand for your reserve hand, or when another player plays an attack, you may reveal this to set this and up to 2 cards in your reserve hand aside. After the exchange has been made return those cards to your reserve hand.
"When you would exchange your hand for your reserve hand" seems super narrow. There are only 1-2 cards that do that so far I think. Without that, even if you manage to buy and set aside 8 of these through attacks, you'll only have 12 cards in your reserve hand, so these are worth 4 VP. That doesn't seem very exciting. It needs to be stronger without other reserve hand interactions.
12.
Network
4
Action
+2 cards to your reserve hand. Put 2 cards from your reserve hand into your hand.
Comparable to Gear, but I think weaker. It's good in the opening to grab the 2 Silvers, but after that? It's just a +2 cards that lets you store away 2 junk cards. I see no reason why this shouldn't cost $3.
13.
The Path Less Traveled
3
Action
+1 Action. You may exchange 1 card in your hand for 1 card in your reserve hand card for your reserve hand. You may play an action card from your reserve hand.
I don't really get this. it's +2 actions, and then +1 card from your reserve hand usually? Without other reserve hand interaction, you will quickly deplete your reserve hand and then this is no use at all. It's too weak even for $2.
14.
Portal
4
Action
+1 Action. Exchange any number of cards in your hand for an equal number in your reserve hand. Then you may exchange your hand for your reserve hand.
This is the same; I don't see it doing much without other reserve hand interactions.
15.
Repurpose
5
Action
Trash a card from your reserve hand gain a card costing up to 2 more than it to your reserve hand.
I guess you could use this to make your Reserve hand all Provinces, but that seems not that amazing. The first 2 plays are essentially +6 VP though if you upgrade the Silvers into Duchies. So it cannot really cost less because it can provide a large amount of VP, but at the same time it's kind of weak after the first two plays. Not sure what to think of that.
16.
Royal Census
4
Action
Reveal an action card from your hand. Set down any number of copies of that action card from your hand or reserve hand. Play that action card once per number of times you set that action card down.
It should probably be "set aside", and you need to clarify what happens with the set aside cards afterwards. It seems rather weak unless you can get to large handsizes, and if I understand your intention correctly, even then all it does is provide a number of +actions equal to the number of equal action cards in your hand. Seems weak.
17.
Signature
5
Treasure
1$. While this is in play when you buy a card you may gain it to the reserve hand.
This is on on-buy Island. I think this was discussed elsewhere? Setting aside your VP buys is just too strong.
18.
Smelter
5
Action
Exchange your hand for your reserve hand. +4 cards to your reserve hand.
So this works as a kind of Tactician. It seem pretty good, and after the first play the worst case is "discard your hand, +4 cards". Not too amazing compared to Minion, but it's more flexible, so I think it could be good.
19.
Storm
3
Action-Attack- Duration
Take 2 cards from your reserve hand. From now until the start of your next turn no one may exchange cards between hand for their reserve hand.
This is again useless unless there are other resreve hand interaction, and even then it's kind of a self-counter.
20.
Supply Line
4
Action-Treasure
+1 Action. Exchange your hand for your reserve hand.
-
Worth 1$ per time you exchanged your hand for your reserve hand this turn.
I don't get it. It's super weak? The exchange will not necessarily be a benefit, and playing like 5 of these nets you $6 at best.
21.
Teleport
5
Action
+1 Card. +1 Action. Set aside up to 5 cards from your reserve hand. +1 card to your reserve hand per card you set aside. Then put the set aside cards onto your deck in any order. You may exchange your hand for your reserve hand.
I have a hard time grasping what this does. I mean every step is clear, but it's hard to assess how good the overall effect is. It basically allows me to nonterminally exchange hand hand for 4 new cards, either ones that are already there, or I can replace the ones I don't want at the expense of the junk going on top of my deck. I think I would need playtesting to figure out how good this is.
22.
Wine cellar
2
Action
+1 Action. Discard your hand. Draw five Cards. You may exchange your hand for your reserve hand.
Even without the exchanging, that seems pretty good for $2. It doesn't quite have the self-synergy of Minion, but it's a super solid draw-to-X card. I would make a case to have this cost $3. Then it's probably quite interesting (but I don't think you'd really use the reserve hand exchange a lot).
23.
Negotiate
5
Action
+2$ You may exchange your hand for your reserve hand. When you buy a non-victory card you may play treasure from your reserve hand to buy a copy of it. At the start of cleanup return the treasures played from the reserve hand to your reserve hand.
I am not really sure what "to buy a copy of it" means. Do you get a +buy that you can only use on that card, or do you just gain a copy? Is "it" the non-victory of the treasure you played? This needs better wording as I don't understand what it does.
24.
Photographer
2
Action-Duration
+1 Action. Exchange your hand for your reserve hand. At the start of your next turn you may exchange your hand for your reserve hand.
It seems not too amazing, but it's probably possible to utilize it.
25.
Imbalance
5
Action-Reaction-Attack
As action: +Action Exchange your hand for your reserve hand
As reaction-Attack: Whenever this card passes from your hand to your reserve hand each other player gains a curse.
If you discard this from play during your cleanup phase you may put it into your reserve hand.
I'm not sure if this should be an Attack type; after all, the actual cursing does not happen as part of the on-play effect. It seems pretty weak; you need at least two of them before you can start cursing, and it doesn't do anything else for you really (the exchanging is not really a positive effect).
26.
Cavalry
4
Action-Attack
For each player (including yourself) select either their hand or their reserve hand. That player discards that hand and draws 3 cards to that hand.
This is a brutal attack and should cost at least $5. Seriously, it's better than the Legionary attack, and that one requires you to line up a Gold first. I would make the case that this card should not exist at all.
27.
Costume Party
3
Action
+2 Cards to your reserve hand.
Each player passes a card from his or her hand to the discard of the player to the left at once. Then each player passes a card from his or her reserve hand to the player to the left's hand at once.
I think this provides roughly as much benefit to all other players as it does to you. Without other reserve hand cards, you may very well end up removing good cards from your deck, so it will even hurt you more. I wouldn't ever buy it unless there is a specific combo.
28.
Hunter's Hideout
5
Action
+1 Card
+1 Action
+ $1
When you trash this gain it from the trash.
-
When you gain this put it in your reserve hand.
This literally does nothing and disappears without other reserve hand cards.
29.
Madman's Shanty
5
Action
Reveal your hand. If there is no
action cards: +2 cards, +2 action
treasure cards: +3 cards, +1 action
victory cards: + $1
That seems hard to use effectively. The "no action" effect is just a Shanty Town (and it doesn't provide the +2 actions unconditionally, so it's even weaker). The treasure effect is good and it has a place in treasureless decks. But that is the only use and it's pretty narrow.
Timer/ The Jack in the Box
This pile begins with 10 timers and 1 The Jack in the Box
Cards may be bought in any order.
Timer
5*
Action
+1 Card
+1 Action
You may put a Timer from your hand into your reserve hand.
-
If this card is in your reserve hand at the start of your turn you may put it into your hand.
-
If The Jack in the Box is in play, this costs $3 and you may gain this to your reserve hand.
The Jack in the Box
When you gain this set the Jack in the box and a Curse in front of you. When The Jack in the Box is in front of you at the start of your turn you may discard a Timer or a Curse, add a Curse to The Jack in the Box, and pass it to the left. If you do not, gain the Curses in The Jack in the Box and return it to the supply.
-
If you buy this you may not buy a Timer this turn.
There have been numerous hot potato ideas. I think this one forces a bit of a degenerate game until everyone is sufficiently protected. It also introduces politics with multiple players.