In general, I think an expansion should focus on some new mechanic, or at least on a mechanic that hasn't been the focus of an expansion before.Personally, I think there's plenty of room for fan expansions that use preexisting mechanics in new ways.
mh, I think the reason this approach is frowned upon is that it tends to what people do when they create cards without putting that much effort into them. it's the most obvious way to go: pick some sort of event or choice, add a bunch of options involving curses and ruins, and also make a duration or overpay effect. however, that doesn't mean that it's inherently bad, in fact I do think that there are enough things left to do with the existing mechanics, and that it's possible to create an exciting expansion using old mechanics. so, i wouldn't say that a new expansion has to come up with new a new theme.
what I would say is that it will feel more like a cohesive whole if it does. there is, as far as i know, not a single card in any existing expansion that refers to a card or mechanic that's not in its expansion or in the base set. it would be totally reasonable for baron or scout to work on shelters, or for salvager to do stuff with potion cost cards, but they don't. it could be considered a waste of potential, but it does have practical reasons.
on to the cards
Cost 3 - Action
Reveal the card that is 3rd from the top of your deck. If it's an action card: play it and +1 action. If it's a treasure card, put it into your hand and +$1. Otherwise, discard it and +1 card.
"3rd from the top" is awkward. I suggest using the bottom card of your deck instead.
Like Iron Furnace, this is too weak. When a card is unreliable, the different options should each be powerful relative to its cost. But this is just a Village, [+1 Card; +$1], and [sift a card; +1 Card], respectively. Super weak! Maybe the Treasure option is fine, but the other two definitely need a buff. Probably all three.
i agree with LF here. this is super weak, and bottom card does seem more elegant. usually, a good way to estimate the powerlevel of a card is to compare it to as many different cards as possible. f.e, a very obvious thing to do in any extension is a terminal silver for $3/4 (LF has one(?) of those, too). Just list all terminal silvers that exist in dominion, these would be
moneylender, monument, navigator, cutpurse, militia, scavanger, chancellor, woodcutter, swindler, nomad camp, fortune teller, conspirator, steward, bridge
and look how it holds up here. if it's stronger or weaker than all of them, it probably needs tweaking, because chancellor is pretty awful and swindler pretty op.
if your card is a terminal silver for $5, you can do the same with all terminal silvers for 5$, there are a bunch.
for this specific card, it's not quite as obvious, but it still works, you only have to think a little bit more. the best card to compare it to is ironmonger. both reveal one card, so let's compare the options.
action card: both are a village, but your card is better because you're guaranteed to make use of the +action. contradicting to what LF said, I think this is the one option that is alright.
treasure card: your card is a peddler without +action, and ironmonger is either a peddler, or more common, a lab if it hits copper. huge difference.
victory card: your card is a moat, ironmonger is a double lab. gigantic difference.
useless non-victory card: your card is a moat, ironmonger is a lab
so, as you can see, the card utterly outclassed, and it's easily recognizable if you just pick the right card to compare it to. and, uh, don't make the mistake of thinking ironmonger is allowed to be stronger because it costs 4$ and your card is $3; 3$ and 4$ are almost identical. it's like 6$-----5$---------4$-3$----2$
Cost 5 - Action - Attack
+2 cards. Each other player must discard an action card or reveal a hand without any actions. If a hand is revealed without any actions, that player gains a ruins. If any ruins are discarded +$2.
the cards to look at here are witch, cultist, ghost ship, and vault. witch and cultist because they both deal out junk, ghost ship because it attacks the current hand, vault because it's a variant of +2$ (and because all of them have +2 cards). it's not as obvious here as it is with the last card though. if it does deal out junk, it's worse than witch and cultist. if it doesn't, it might be worse or better than ghost ship. if it hits ruins, it's about as good as vault without the drawback of helping your opponent.
let's compare some scenarios in 2p
opponent doesn't have an action card: weaker witch/cultest. worth mabye 4,5$
opponent does have a strong action card (f.e. another vandal): very strong attack, worth about $7
opponent has a weak action card in hand like a single village: mediocre attack, maybe 4,5$
opponent discards a ruins: about as good as vault, might hurt him a little bit too. worth about 5,5$
overall this looks pretty decent. it's unique too. the only problem would be the harshness of case #2, i.e. swinginess if you discard your opponents vandal. sea hag can do that too, but it's less likely, and it also sucks anyway.
Cost 4 - Action
+$1. Reveal the top 4 cards of your deck. Put a revealed victory card, curse, or ruins into your hand. Put a revealed treasure into your hand. Discard one other revealed card. Put the rest back in any order.
okay, i'd mostly look at smithy here. you get the best treasure card out of 4. you get to discard one or two bad cards out of 4, and you get +1$. that isn't clearly better or worse on first glance, so let's take some samples
let's say the cards on your deck are silver, silver, estate, copper. smithy would net +4$ and leave a coper on top of your deck. mine scout would net +3$ and leave a silver on top of your deck.
let's say you have gold, copper, province, estate. smithy is +4$, leave curse on top of the deck. your card is identical
copper, copper, estate, copper: also identical...
mh, so if there are 3 treasure cards, and 2 of them among the first 3 cards, the difference between smithy and your card is 1$ minus the second best treasure card. if that card is a copper, it's identical to smithy, if it's silver or better, it's worse.
if there are 4 treasure cards, you also have to substract the third best treasure card. your card will be better if there are action cards though, because you can put the best ones back, while smithy will just draw them dead. if you reveal a dead card, two action cards and a treasure, you will net +1$ +$ from the treasure, discard the bad action, put the better one on top. smithy will have a random card on top and just +$ from the treasure.
so, in conclusion, your card is slightly worse than smithy in BM strategies but better in slogs. oh, and naturally it's terrible in engines because it can't draw action cards.
yea, hm, dunno what to make of that. but I do hope i gave you some ideas for future evaluation.
I agree with LF on marketting agent. I don't think there is any single card that can justify different tokens.
Cost 6 - Action
If you have no actions in hand, reveal your hand, then reveal deck cards until you reveal an action, put the action in your hand and discard the rest. Choose an action card in your hand. You may play it once, twice, or if it costs less than $4 and isn't an attack, you may play it three times.
(you need to tweak the wording so players can't dig for actions even if they have action cards in their hand.)
this is reallly swingy. dig for an action card, play it twice, that's about as good as a golem, a card which is worth at least $7. dig for an action card, play it three times, that's insane. so, if you play something like sheme/R.A, each r.a. is a guaranteed +3 cards, +3 actions, and you can always top deck all of them. it's so good that you probably never want to buy any terminals, so that you can always dig for stuff. also, I don't see any reason for the "isn't an attack" part.
a more reasonable version would look like this:
Choose one: dig for an action card; or choose an action card from your hand, if it's worth 4$ or more, play it two times, otherwise, play it three times.
Cost 3 - Action - Reaction
+2 cards. Set aside a card from your hand. Put it into your hand next turn.
When another player plays an attack card, you may reveal this from your hand. If you do, the other player sets aside the attack card after it resolves and discards it after his next shuffle.
the top part is heaven effect on moat instead of on a cantrip. since terminal draw is exactly what makes a heaven effect good, it's reasonably strong on its own. it's kinda similar to courtyard, but it seems to be better.
the reaction part is interesting on first glance. your opponent plays a taxman, you put him in jail, but you have to pay the taxes anyway. it's definitely a funny theme. i'm... not sure if this hurts enough to ever make people not want to play attack cards, but i can absolutely see situations where the reaction can be huge. say your opponent plays a rabble/village engine. with just one prison, you can put all of his rabbles in jail, and he has to grind through his entire deck without them, causing him to have maybe 3 or even 4 dead turns. since +3 card + attack is not a rarity, I don't know if there is any way for you to balance the reaction. you could make it work just once, but then it becomes political. you could make the prison just hold one spot for each player, so that if he plays another attack card, his old one is discarded. that might work.
so, uh, I have listened to an entire album while writing this. I'll take a break, maybe I'll comment on some of the other cards later.