Keystone is a pub game in Fable II and Fable II Pub Games that is described as a mixture between Roulette and Crappes. In this game, the player bets on the tiles of a board shaped as an arch. These bets, called "arch bets", are placed at the start of the game on any number from 3 to 18 and are kept until they are won or the game ends. Then the player makes "inside bets", which are effective only on the present turn and can be repeated in future turns. Inside bets can be placed on any number from 3 to 18, a range of numbers (4 to 9, 10 and 11, or 12 to 17) or a group of numbers (red, black, even or odd). The player may also bet on other different combinations. The player then rolls three six-sided dice, the addition of which is a number on the board.
Each time the dice are rolled, the resulting number is removed from the arch. If this number is rolled again, then an adjacent tile is removed. A lower number is removed if the result is 10 or less and a higher number is removed if the result is 11 or higher. The game ends when all the tiles have been removed, if both keystones (10 and 11) are removed or if one base stone (3 or 18) is removed. If a 3 or 18 is rolled in the first turn, it is a Jackpot; all Arch bets are paid and the game is over. Payouts depend on the probability of the rolling the number or combination specified.
Keystone may be played in the Cow & Corset Inn in Bowerstone Market and in other locations. In Bloodstone, a variation of Keystone is played. It is called Bloodstone and the player bets against the die rolls. In Bloodstone, all bets win the player 10 gold, due to the greater probability of winning. However, if the player loses a bet, the amount lost is greater. The payouts can be checked using the odds button (left trigger) while playing.
The payouts offered for arch bets are different in different locations and change with your gambler level.
The following are the minimum payouts for which the various tiles are worth betting, calculated by a computer simulation. (The random simulation is why the odds don't exactly match on the left and right.) For example, to make it worth betting on the 3 tile in keystone, you want odds of 184:50 or better, whereas for Bloodstone you want odds of 50/183 or better. (Divide both numbers for different minimum bets, for example tile 3 would be 92:50 or 25/91.)
Note in particular that 8 and 13 are far more likely to be removed than you'd guess -- more likey than 9 and 12, despite being rolled less often than 9 and 12. Because the payouts offered in-game usually increase as you go down the sides from the keystones, this fact is usually what makes you money. At the Cow & Corset, on some of the levels it's advantageous to bet on all the tiles except 7, 9, 12, and 14.