15 ○ 9 × 2015

15 ○ 9 × is a two-player deduction game, with each player trying to deduce — and identify through card play — the pairs of cards laid down by the opponent.

The deck consists of 15 ○ cards and 9 × cards. Each player receives ten cards from the deck at random, then creates three pairs of cards, leaving the remaining four cards in hand. Each player now tries to correctly identify whether each pair of cards played by the opponent matches (in which case you need to play a ○ on the pair) or whether they don't match (in which case you need to play an ×).

Instead of making a guess, you can reveal one of the cards in one of your pairs, giving up information but delaying the need to guess.