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!