Please add "IMHO" in front of everything I say.
Sewer
Action - $2
Reveal the bottom card of your deck. +$ equal to its cost in coins.
This had already been pointed out, but the card has to be discarded, otherwise this is nuts. Even if the card is discarded, this might still be too swingy. At least add a condition on the card being an Action or Treasure. So for example:
Sewer
Action - $2
Discard the bottom card of your deck. If it was an Action or Treasure card, +$ equal to its cost in coins.
I like the flavour though.
Secret-Keeper
Action - $3
+2 Cards, +1 Action
Put a card from your hand on the bottom of your deck.
This is actually very strong. Putting a card on the bottom of your deck is nearly as good as discarding it, because the card will likely miss the reshuffle, and apparently +2 card +1 action discard a card is very strong at $4, so this would likewise be strong.
But it gets even better when you realize that you can use this to set up combos as you go through your deck. You can make sure that your last turn through your deck will have a village and a smithy or whatever. Sort of like a delayed haven without the handsize increase or decrease.
Looks like a very versatile card. I like it.
Double Agent
Action - $3
Play this as if it were an Action that the player to your left chooses from the Supply (other than Double Agent) costing from $3 to $5. This is that card until it leaves play.
Mrmmrmmm... Yeah, not really convinced here, sorry. Maybe as a $2? Buff it, add +1 action? Even then, you won't be happy when your opponent chooses Trading Post late game... I don't see how the concept can be reworked into something that is more interesting than the worst possible card you could have in your hand...
Lordling
Action - $3
If you have an even number of cards in hand, +$2. Otherwise, +3 Cards.
This is
sooooo coooooool. No idea if it is balanced, but
soooooo cooooool.
Note that with "regular" villages, after the first Lordling, all of them will be smithies.
Ancient Amulet
Action-Attack - $5
Gain a Silver, putting it into your hand. Each other player reveals and discards the top card of their deck. If it is a Victory or Curse card, they gain a Curse. Otherwise, they gain a Copper.
Not super exciting, but then again, cursers rarely are.
Leap of Faith
Action - $4
+1 Action, +$1
The player to your left picks a number from 1 to 5. Reveal that number of cards. Put the last card revealed into your hand, and discard the other revealed cards.
So a peddler that will start cycling like crazy once you start greening? Ok, why not. Not sure if it's
that interesting though.
Fence
Action - $4
Trash up to 3 cards from your hand. +1 Card per card trashed.
Yeah, crazy crazy strong. You are pretty much guaranteed to open this, maybe even get Fence/nothing if you open 5$/2$. This wants some sort of penalty somewhere to make it slower. Be creative
Bastard
Action - $3
Discard a card. You may play an Action (other than a Bastard) from your hand 3 times.
When you gain this, gain a Curse.
So many penalties! Then again it's KC. Kinda hard to evaluate without actually playtesting it. This is based on the (arguably) strongest card in the game after all, and it only costs $3.
Jailer
Action - $5
Look at the bottom 4 cards of your deck. Put up to 3 of them in your hand, and discard the rest.
So, two things: looking at the bottom of your deck takes longer than looking at the top of your deck (anyone want to make a stack joke here?), so a smithy that looks at the bottom of your deck
and makes you choose is going to be extremely annoying with villages.
The other thing: other than
edgey edge cases, is there a reason why you would want to put less than 3 cards in hand? Why is that even an option?
There might be something here, but it needs a lot of work.