### Analyzing the Mirror Deck for Game Design

It's been a few years since I created the Mirror Deck and posted it on DriveThruCards. As a reminder, it's a deck of cards numbered 1 through 99, where each number can have its digits transposed, so the deck is only 54 cards. I asked some advice from other game designers recently on where to take the deck next. James Ernest was especially helpful, recommending that I look for any rarities or natural "sets" in the deck that would lend themselves to game mechanisms.

I'm looking at how I can make a two-player trick-taking game out of the Mirror Deck.

## Triangular Numbers

There are 13 triangular numbers in the deck's range, which I could mark with a triangle "suit" icon.

1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91

## Perfect Squares

There are 9 numbers in the deck's range, which I could mark with a square "suit" icon.

1, 4, 9, 16, 25, 36, 49, 64, 81

## Primes

There are 25 prime numbers in the deck's range, which I could mark with a "P" icon as its own suit.

2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97

## Differences

The main hook of the Mirror Deck is how you can treat each card as a higher or lower value. It would be useful to know the maximum difference of any two inverted numbers.

• Difference: 0 (9 Cards): 11|11, 22|22, 33|33, 44|44, 55|55, 66|66, 77|77, 88|88, 99|99
• Difference: 9 (9 Cards): 21|12, 32|23, 43|34, 54|45, 65|56, 76|67, 87|78, 98|89, 10|1
• Difference: 18 (8 Cards): 31|13, 42|24, 53|35, 64|46, 75|57, 86|68, 97|79, 20|2
• Difference: 27 (7 Cards): 41|14, 52|25, 63|36, 74|47, 85|58, 96|69, 30|3
• Difference: 36 (6 Cards): 51|15, 62|26, 73|37, 84|48, 95|59, 40|4
• Difference: 45 (5 Cards): 61|16, 72|27, 83|38, 94|49, 50|5
• Difference: 54 (4 Cards): 71|17, 82|28, 93|39, 60|6
• Difference: 63 (3 Cards): 81|18, 92|29, 70|7
• Difference: 72 (2 Cards): 91|19, 80|8
• Difference: 81 (1 Card): 90|9

I can use a dice face symbol to note the number of cards in each of those suits, for example the Difference:36 cards would have a ⚅ symbol because there are six cards in that set.

## Multiples of 11

One thing I noticed from the beginning is that a multiple of 11 has the least flexibility in the whole deck, since it cannot create a new number by transposing its digits. In most game designs, I'd probably set this set aside with some special rules. For example...

• A dummy leader in a two-player trick-taking game: Shuffle up the 11s into their own deck. Reveal a new card at the start of a trick. This is the lead card.
• Stakes of a round: The game is divided into 9 rounds, each worth progressively more points. The first round is worth 11, the second worth 22, and so on. The winner of a round takes the card into their score pile.
• Trump Cards: I could just say that these nine cards "beat" any other card in a trick. A trump card can only be beaten by another trump card of higher value. So 11 beats any normal trick, but 22 beats that, and 33 beats that, and so on.

I think I'll go with the last option since it keeps things flexible.

In a future post, I'll write up the rules to a trick-taking game using the Mirror Deck. Stay tuned!