This week it is all about being in play. Design a card or landscape that in someway cares about what you currently have in play.
I deliberately gave a loose definition "someway cares about what you currently have in play" as I want to give a lot of freedom. For example, it could be behavior dependent on how many cards you have in play, types of cards you have in play, look to see if a certain card is in play, etc. It could happen when you play the card, or it could be an on gain/buy/trash, etc, effect. You can interact with cards in play, for example trash them, replay them, gain a copy, etc. You could have a card whose properties are changed by what is in play, e.g. Peddler. Conditions on whether or not you can buy or gain a card could be dependent on what is in play, e.g. Grand Market
Below is a list of official cards that I would have deemed acceptable if they didn't already exist. Note the list is not necessarily complete, I might have overlooked something.
Cards
Bank
Changeling
Conclave
Conspirator
Crossroads
Emporium
Fortune
Grand Market
Horn of Plenty
Idol
Leprechaun
Mandarin
Magic Lamp
Mint
Monastery
Peddler
Raider
Scepter
Soldier
Tormentor
Warrior
Events
Alms
Bonfire
Pilgrimage
Raid
Stampede
Landmark
Colonade
What I would not accept are cards which affect cards played after it, for example, Sauna turning subsequent Silvers into trashers and Urchin's effect if the next card played is an attack.
Good luck.
*Soldier added to the list of official cards that would be valid, thanks Spineflu.