Here's an interesting idea for the Design Contest: Design a card with a mechanic that's not yet used in the game.
You could use dexterity (a bad idea, but go for it if you will), passing the card you played to your neighbors, a card that's an action on one turn and a treasure on the next, etc....
The card still has to fit within the rules of the game and be playable with any of the other cards currently available.
Some cards with unique abilities currently in the game: Masquerade, Possession, Black Market, Young Witch, Native Village, Island, Pirate Ship, Haven, Tactician, Tournament, Band of Misfits. If we loosen the definition, the list could be bigger, it doesn't matter really.
What I mean is that we've seen cards that reveal, have an on-something event, give cards, actions, buys and coins in some way, discard, trash, gain, etc... You could call Pearl Diver a unique card, because it's the only one that lets you look at the bottom, but it's just another form of revealing.
I'm just curious as to what unexplored space there still is and challenge all designers to boldly go you-know-where.
Thoughts?
An example:
Tax Collector
Action-Duration $2
Discard a Treasure card from your hand.
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During the buy phase of your next turn this is played as a Treasure giving as much $ as the Treasure discarded.
Don't pay any attention to the wording or any rule weirdness or whether it would be actually useful, it's just an example.