Here's another custom card I've tested and enjoy. It's not a power card but does add some flavor. The difficult thing is the text is long, but the concept is simple enough.
Magistrate
$4 - Action/Reaction
+$2. Look at the top 3 cards of your deck. Discard any of them that you choose and return the rest to your deck in any order.
When another player plays an attack card, look at the top 3 cards of your deck. Discard any of them that you choose, return the rest to your deck in any order, and set this card aside. At the start of your next turn, return this card to your hand.
Disregarding the reaction effect for the moment, this is comparable to Navigator. It's the same price, offers the same terminal Silver benefit, and allows you to keep or discard cards that will come up in your next hand. But whereas Navigator is an all-or-nothing deal, Magistrate allows you to selectively keep or discard specific cards. In exchange for this finer control, you can only do this with the next 3 cards instead of the next 5.
The reaction effect was an afterthought: I thought, hey, this is good, but it would be nice to be able to do this in response to a top-of-deck attack. It's not quite as robust against Pirate Ship, Thief, and especially Fortune Teller, but it will often still do the job. For example, if someone plays Pirate Ship, you might draw Copper-Estate-Estate. Discard the Copper, return two Estates, and then the attack will discard the Estates harmlessly. On the other hand, you might draw Copper-Copper-Copper, in which case the best you can do is discard them all and hope that the two cards AFTER that don't also contain a treasure.
It's also good against the discard effect of Sea Hag, ensuring that the card it discards isn't an important one.
But the main purpose of the reaction is not protection against attack at all but rather the ability to do is thing without spending an action on it when your actual turn comes around. You miss out on the +$2 that way (unless you want to do it again), but it allows the card's effect to be used even in a terminal collision with a stronger action card.
The set-aside mechanic, borrowed from Horse Traders, is quite necessary, as otherwise you could reveal it infinitely, potentially cycling your deck many many times, until you stumble upon a shuffle that bunches your best three cards together. Very broken.
I think it's well-balanced at $4. With the reaction effect, it compares favorably with Navigator, but Navigator is on the weak side of $4 anyhow.
