Idea to Concept: Moonflight
I admire the simplicity of an elegant design idea, hopefully most games designers and developers do. The concept of a deck builder is extremely elegant. The act of building a deck is satisfying and includes action, engine and scoring in a single simple act. So it goes on the quite short list of ideas I wish I had been able to come up with.
However, there are a few gaps in this very elegant design. One of the biggest is that just as players get their deck built the game tends to end, which can be quite unsatisfying. This is usually compounded by the scoring of deck builders which is based on counting through the built up deck in slightly fiddly fashion. Sadly most games which seek to remedy these problems simply tack on a "something to do with the deck" second act which undermines the very elegance which makes the deck builder so perfect as a game design idea.
So my big idea was a deck un-builder where the game ends when a player tries to draw but cannot, even with a reshuffle. Once the game ends players score only the cards in their hand. However, for a long time the concept of handing players a deck pre-built and asking them to un-build it sat uncomfortably. Still, the idea of un-building a deck was quite clear and the different deck's themes wrote themselves. One deck would extend a player's hand, one would build a tableaux, one would return trashed cards, one would hand their cards to an opponent. This also slotted quite neatly into a vague fantasy setting; scholar, builder, grave digger and thief.