History: 12 (also known as Jamaican Sniping) was invented at the beginning of June 2009 by a cabin at Yosemite. The game was devised by Sam Levey who contributed this description, Juan Campos, Thomas Zachariah, and Aaron Uh.
This game works best with 3-6 players, although it could be played with 2 or 7. A standard 52-card pack without jokers is used. Suits are ignored in this game.
Each player is dealt 5 cards by the dealer. The remaining undealt part of the deck is stacked face down. Each player takes turns starting with the dealer's right, going away from the dealer (counter-clockwise). To start, a card is flipped over from the remaining deck and placed faced up for all to see. This begins the play pile.
The player whose turn it is must play face up on top of the play pile. If this card added to the card it is played on makes a total of 12 (J's, Q's, and K's are worth 11, Aces are worth 1) or makes "doubles" (the cards are equal in rank) the player takes the pile. So for example if the card is a 4, the player would either play a 4 or an 8 to take the pile. Playing a face card on a different face card does not make a double even though both are worth 11, so if the card is a jack the player would need to play a jack or an ace to take the pile, but not a queen or king. If the player makes 12 or doubles, he or she takes the pile, lays it off to the side. Another card is flipped from the top of the deck, and the player takes another turn.
If the player cannot make 12 or doubles, he or she must play another card (anything) and then draw a card. As as result, the only way to lose cards in your hand is to make 12 or doubles and take piles. If the player fails to make 12, then it is the next player's turn.
For the next player, and each subsequent one, only the card on the top of the pile of face up cards is taken into consideration, however if 12 is made, the whole pile is taken. For example, if the pile is, from bottom to top, 2, Q, J, 4, 7, and I played a 5 or a 7, I would take the entire pile.
If any player runs out of cards in their hand, the game is immediately over. If the deck runs out first, then the game goes around one more time: if anybody takes the current pile, the game is over, or if not, the game ends on the person who drew the last card. If the last cards are drawn and there is no face up pile, then the game is immediately over.
A special circumstance occurs when a player makes 12 with a 6. Since 6's are both 12 and doubles, they are special and rare, and when that happens, every other player must draw one card from the deck, going to the right. If the deck runs out before everybody finishes drawing, the game is over, and those who did not draw got lucky.
After each round, the score should be totaled: a player's score is equal to the number of cards they have picked up MINUS the number still in their hand at the end of the game. (Note: you do NOT count the value of each card: only how many cards there are.) The lowest possible score, then, is -7 (you never made a double or 12 and two double 6's were made by other players). It is possible, though rare, to score 20 points or more.
If you are playing multiple rounds, then you may either total the score and end up with a cumulative winner (it is customary to play 12 rounds of 12) or simply note the winner of each round. If multiple rounds, then the dealer should be rotated to the left, and if desired, players may alternate the direction in which the game is played.