I've somehow overlooked a family of two-player card games that require only a standard deck and are playable in many situations: Gin Rummy and friends. I had tried playing before but I never appreciated them until recently, when a veteran taught me an interesting variant, and repeatedly beat me easily. At first, that is!
Apparently, this variant is popular in Thailand, but I have yet to see these precise rules described elsewhere, though 500 Rum comes close.
Deal: I believe the first dealer is determined randomly. In following hands, the loser of the previous hand is dealer.
The dealer deals 13 cards to each player, and places the remainder, the stock, face-down. The top card of the stock is placed face-up in between the players to start the discard pile. The non-dealer goes first.
One aims to meld all cards in hand, either in sets: 3 or 4 cards of the same rank, or in runs: 3 or more cards of the same suit in sequence. A card can only be melded once, so it is impossible for it to count towards a set and a sequence. Aces are always high, and 2s are always low, so in particular A-2-3 is an invalid run.
Play: Each turn consists of three phases:
1. Draw: a player can take a card within the discard pile, if they can use it to form a set or run with at least one card in their hand and optionally using discards further up in the pile, and additionally if they take every card lying on top. They must display the meld, by laying it on the table in front of them.
In other words, they take some number of cards from the top of the discard pile, and use the bottommost card taken in a meld, which must then be exposed immediately.
If a player is unwilling or unable to take any cards from the discard pile, they must draw a card from the stock, unless the stock is exhausted in which case the player must pass. If both players pass, the hand ends.
2. Meld: the player may display on the table as many melds as desired from their hand, so long as they have at least one card left in hand. They may add cards to existing melds belonging to either player, but in both cases the cards are placed in front of the player extending the meld.
3. Discard: the player must discard one card. If it is their last card because all their other cards have been displayed, then it is placed face-down on the discard pile and the hand ends. Otherwise it is placed face-up on top of the discard pile and off to one side, so that every card in the discard pile can be seen at all times.
Scoring: A player receives 50 points for placing a card face-down on the discard pile, that is, when they have melded all their cards save one which becomes the discard. They are considered the winner of the hand, even if they ultimately have a lower score. If the game ends but both players still have cards, the winner is the player with the higher score.
A player adds the values of the cards displayed in front of them and subtracts the values of the cards remaining in their hand: cards of rank 2 to 9 are worth 5 points each, 10, J, Q, K are worth 10 points each, and Aces are 15 points each, with two exceptions. Both the Queen of Spades and Two of Clubs are worth 50 points.
Typically a hand ends because one player has melded their entire hand, and only one player subtracts the values of cards from their total. Both players subtract values of cards only when a hand ends because both players have passed.
There are two "stupidity" penalties. Firstly, if a player wins by melding their whole hand after taking just the top card of the discard pile, that is, the opponent's last discard, the opponent subtracts 50 points from their score.
Secondly, during the game, when a player discards a card that could have been used to extend an exposed meld, that player loses 50 points. The penalty is cumulative; each offence costs a player 50 points.
Lastly, there is a doubling rule: if a player does not display any melds except possibly in the final turn, their score for the hand is doubled. So if a player wins by melding their entire hand, and had not previously displayed any melds, their score is doubled. This is almost always beneficial because they usually have a positive score. And if a player wins by melding their entire hand and their opponent has not yet displayed a single meld, the opponent's score is doubled. This is always harmful to the opponent because they must have a negative score, seeing as no melds were made and cards remain in hand.
Winning: The final score is added to a running total. There are two victory conditions. If a player has -500 or fewer points, their opponent wins the game instantly. Otherwise the first player to have 500 points or more after going out wins the game.
More players: if there are a few more players, deal three fewer cards per extra player.
Summary for those familiar with rummy games:
- Aces always high, 2s always low
- Can take variable number of cards from top of discard pile; must use the bottommost card taken
- Must make a new run or set with this card; cannot just extend existing meld
- Must meld with at least one card in hand with this card
- Boathouse rule: must discard when going out
- Hand ends immediately after a player goes out
- 50 pts for going gin
- -50 pts for giving opponent single discard used to go out
- -50 pts for discard card that could augment a displayed meld
- Score doubled for never displaying melds
- Values of cards: 2-9: 5 pts, 10-K: 10 pts, A: 15, except QS, 2C: 50 pts.
- -500 pts loses the game
- 500 pts insufficient for win; must also go out