Sly Fox is a solitaire card game played with two decks of 52 playing cards each. It is probably named because the player has to be "sly as fox," so to speak, to win, if played correctly.
First, one king and one ace of each suit are removed. The aces are placed vertically on one side of the tableau, the kings are placed on the other side. These form the foundations.
The rest of the cards are shuffled and twenty cards are placed between the ace-foundations and the king foundations. These 20 cards form the reserve and are available to play only onto the foundations. The aces are built up, while the kings are built down, all by suit.
Gameplay is divided into three phases.
The first phase involves moving the cards from the reserve to the foundations for building only. When a card leaves the foundation, the gap it leaves behind is immediately filled with a new card from the stock. When all possible moves are made, or when the player had done all the moves he can make, play moves to the second phase.
The second phase of gameplay involves dealing 20 cards from the stock, one at a time, to any of the 20 piles (the cards already there serve as bases) on the reserve. It does not matter where each card ends up; a pile can contain more than two cards while a pile would end up with just one card. In this phase, no building is allowed until all twenty cards are deal. Once the twenty cards are dealt, gameplay moves to the third phase.
The third phase is similar to the first phase, moving cards from the reserve to the foundations. The top cards of each reserve pile are available for play. This time though, when gaps occur, they are not immediately filled. Furthermore, the cards on the reserve are not built on each other; they can only be transferred to the foundations, and cards on the foundations cannot be moved once built. When all possible moves have been made, or when the player has made all moves one can make, gameplay moves back to the second phase.
During this deal of 20 new cards, the player has the discretion of filling the gaps left behind during the third phase. When all twenty cards are dealt, gameplay shifts to the third phase. The second and third phases are repeated until the stock has been used up.
The game is won when all cards end up in the foundations. As mentioned earlier, if done correctly, it can be won; but chances of doing this are low.