Hey, cool cards!
Army: The opportunity cost here is huge, but the effect gets insane when you start playing multiple Armies per turn. My worry is that getting to the point where your deck is all Armies and your turns are just playing Armies doesn't seem particularly interesting.
Heir: It isn't very difficult to build a deck that consistently makes $9 per turn, and that's also something that you often want to do anyway, at which point these are just way too good. It seems quite similar to Grand Market in that you have to build up payload before they do anything, except these are easier to gain and give a bigger payoff than GM and it's arguably easier to hit $9 that to hit $6 with no Copper (that depends on the board I guess). I think this could give +$2 and cost $6 and it'd still be quite strong.
Royal Decree: This reminds of Fortune, nowhere near as crazy as Fortune but these do stack really well so they have that going for them. Looking at the player to your left will reduce the effect of multiple opponents and this should probably use wording similar to Necromancer and Army (playing the cards but leaving them in opponent's hand) to avoid nasty interactions with Bonfire/mandarin etc. I'm not sure this really needs the on-gain bonus though? All it really does is make this pay off some of it's debt immediately and it seems strong enough without it. Also I'm npt sure $3+8D is really different enough from 11D to be worth the weird cost?
Moon Shrine: My first reaction was that the +2 Coffers is too good on a non-terminal $3 next to Silver. Although the Vp part is probably more of a drawback than a bonus given that the opponent will have the 1st chance to buy the card with a token given that this is a Night, and this isn't as good as Silver at hitting $5 on the 1st shuffle because you need to draw this turn 3 to be able to make use of the Coppers before you shuffle on turn 5. I guess play testing showed that it was in fact too good though, although I don't think playing things vs big money is particularly useful. Edit: Much to the chagrin of the dominion discord community it's +1 Coffers not +1 Coffer.
Slumlord: Cool card, might end up being too strong though, even just playing something as weak as a Pearl Diver after this is basically giving you a Lost City effect. Perhaps having to draw your cards in the correct order will keep it in check but it seems much easier to do than herald or Diplomat (similar $4 conditional Lost City type things). That isn't even taking into account playing stronger actions with it.
Stadium: This should perhaps tell you to remove the tokens when you discard it from play? My concern with this is that it's basically a guarantee that you can make +$1 with this. That baseline of +$1 is already a Caravan Guard, and the upside of potentially being able to make +$2 or more once you've built up a bit seems much better than the Caravan Guard reaction.
Lost Temple: I think without the using up a Buy part this would be a strong card, but in line with Steward. With the playing it twice thing this becomes pretty crazy I think, it's basically Chapel that becomes a cantrip later, because if you're trashing 4 then you weren't using that Buy anyway. If there are abundant extra Buys then this can basically become a Lost City later too, yikes. I think that's enough to push this up into $5 territory? If you couldn't choose the same option twice then I think it might be okay at $4 though.
Industrious Village: Hmm a lot of conditional Lost Cities here, also I've noticed a lot of these cards that involve jumping through some sort of hoop are rewarding you for doing things that Dominion rewards in general - e.g. Heir rewarding you for building big, Stadium for adding expensive cards to your deck/trashing starting cards and now this for trashing your Coppers and buying lots of Actions. Not that this is necessarily a bad thing, just thought it was interesting to point out.
Old Witch: Now as opposed to rewarding you for what you're doing anyway we're punishing people for doing something you didn't want to do anyway . It's perhaps worth noting that this doesn't actually hurt the opponent's deck until they choose to buy a Victory and let the Curses in, that makes this quite weak imo. Well I prefer weak Cursing attacks where it isn't obvious when to go for them to Mountebank-esque things so that isn't really a problem in my book.
Crane: This has to be at least a $5 right? And probably a $6 really, the top part is strictly better than Lab and even lets you use all unused Actions you have so I can't really see the drawback coming into play very often. And really this is just looking at it on its own, taking into account how well this plays with other sources of +Action and it seems clear that $4 is way too low of a cost?
Mimic: Well the setup here is weird, makes games almost impossible to 3 pile for one. I guess that there would have to be 72 Mimics to account for a 6 player game with Young Witch+Ruins (12 action supply piles!). I'm not sure whether the on-play of this actually works within the rules, Band of Misfits things are always a bit of a danger zone. I think it needs an "this is that card until it leaves play" too to match Band/Overlord. Being able to be any Action is probably dangerous too, might want to put a limit on that. Potion cost is a clever way to make it difficult for the player uncovering these to buy them all up before other players have a chance.
Blockade: I personally don't think I'd enjoy playing with this, having to make this decision once at the start of the game seems like it could take a while to think through, doing it 3 times will slow the start of the game to a halt. I don't much care for the gameplay either, with the choices being hidden it'll be impossible to play around and just come down to the shuffles whether you get the points for it. If you got the points for gaining one of your choices at least you could play towards it. But if you enjoy that kind of thing then go for it!
Thanks for the input Gazbag. I was just looking at some of your cards and I'm quite impressed. They are generally straight forward and anyone using them should have an easy time knowing what to do with it. My cards.... not so much. I'd like to respond to a few of things (not all though since it is quite late currently).
Army - You nailed this one, but I should state that my playtesting has shown in standard games that you can get about 2-4 cards on your Army mat and 2-4 Army cards by around turn 13 or so. Army is a powerhouse at this point, but the game is generally about over and any more building might cost you the game. So yes, getting 5-6 Army cards and having them beefed out would result in some boring games, but a skilled player should be able to beat an opponent trying to overbuild Army (at least this has been the case in my limited testing; edge cases are sure to exist).
Heir - I can see a point for making this cost $6. It's true that hitting $9 consistently shouldn't be too hard on most boards, but it takes longer when you have to spend a bunch of money on Heirs that won't do anything for awhile. Kind of another overbuild card, but as an underbuild kind of player, I think I can punish an opponent going for too many of these.
Royal Decree - You and Aquila both brought up the Mandarin/Bonfire thing and my first reaction was "That is freakin' awesome. Why didn't I think of that!?" Well, it was of coarse an unintended use of the card and I removed it (v0.2). Probably no way to make that a viable in another card right? The on-gain effect is the core of the card. Everything else about it really revolves around this and not the on-play ability.
Slumlord - Everyone seems to love Slumlord. What does that really say about you people?
I also really like how it plays, but can see games where it is too strong. Of coarse that's kind of Dominion for you. Some combos are ridiculous, just hopefully fun and somewhat fair at the same time. But hitting Slumlord and Swindler turn 3! Ugh, so sorry world.
Stadium - This is probably my most tested card and I'm confident in saying it's balanced. Caravan Guard is actually weaker than Silver and without the reaction is sub-cost $3. It's the reaction that makes it more useful. So yes, Stadium hits $1 easily early on, but that's not very good for the price. The $3 to $4 range is where the real value is, but don't forget you can completely whiff with this and get $0.
EDIT My first version specifically said to remove the tokens, but it seemed unneeded. I think people will in general know to discard them and to help with the people who are unsure I will address it in the expanded rules.
Lost Temple - Like Chapel this card is way under priced for it's power, but on purpose. Also like Chapel, Lost Temple needs other cards to work well. Having +Buys certainly helps turn it into Lost City's, but those are hard to come by in cantrip form. And lastly like Chapel, I wanted every opening hand to have access to it, so $4 seemed fair.
Old Witch - Yeah, the delayed reaction makes this one manageable, but having 10 Curses waiting in the shadows for that first Victory buy is scary. There are ways around this, but I think Old Witch is still something to be feared. You do give up a lot to open with them though, so it seems balanced.
Crane - Always thought this should be $5, but changed it to $4 for some reason. Haven't playtested this one yet, but I think the -1 Card token will definitely sting a bit in a mirror match. Playing as Laboratory is nice, but drawing blind could leave you with that last Action and a -1 Card token. Playing as Smithy saves you from that, but may draw Actions dead. These are at least the decisions I was hoping a player would need to consider with it.
Mimic - 72 Mimic cards and you might never see a single one! Haha. Thanks for doing the math on that! I knew it would be a lot, but never bothered to get a number. Certainly a card that will never be published, but thank heaven for blank cards! I had the "this is that card until it leaves play" text in it at one point, but cut it for the sake of brevity. I don't think it actually needs it. I believe it just changes how it interacts with some gaining cards like Changling and Disciple. For instance if you Disciple an Overlord, you don't gain an Overlord, but the card Overlord was played as. Disciple a Mimic and you actually gain a Mimic, which I'm fine with. They are so hard to buy, I think a few edge cases for gaining them is fine. Of coarse I may be wrong and would love to hear if I am.
Blockade - I completely understand about Blockade. When I first made it I thought, "What the hell did I just make!" I was very nervous about it for a long time, but after a few games, it became quite natural to play with. I generally like to spend 4-5 minutes analyzing the board anyways so this certainly fits right in with my play style. I think most boards are quite predictable so there should be some easy points, but it also opens up opportunities to go for unusual combos where your opponent has not likely placed anything. If you ever want to try it, maybe agree to place everything within the first 5 cards to lessen the fear of giving your opponent 6-10 points. Or maybe this is something I should just put into it?
Well thanks again for the comments. I'll have to get back over to your cards soon and post a few things. Maybe even play test some stuff. Take care!