The Two-Deck Game

A quick dive into the game design behind the resolution system of my upcoming TTRPG.

Two decks of cards. One has a red back, one has a blue back.

I am drawing a card from a single, complete deck. In order to "Succeed", I have to draw a card that matches the suit I name: hearts. Assuming no jokers, there are 13 of each suit in the deck, so the odds of calling any single suit correctly on a draw are 13/52, or 1/4.

I draw the Queen of Hearts, and succeed

Easy, right? Good. Now let's change it up a bit. This next time, let's imagine this in the style of a deck-builder. The full deck of 52 cards are face up in the middle of the table, and each turn I can choose one card to add to my sub-deck. At this point in the game, I have only 2 cards in my hand: the Queen of hearts, and the 7 of Spades. I've shuffled my deck, so I don't know what order those two cards are in.

Let's try the call again. In order to succeed, I need to draw a card that matches the suit I name. Now, obviously, the odds are much simpler: a clean 50/50. I call spades.

I draw the Seven of Spades, and succeed

Ok. Let's try one more scenario. This time is the same as last time. I have two cards in my deck, that I know are the queen of hearts and the 7 of spades. But now, there's one more twist: someone else has taken one card from a separate deck, and shuffled it into mine.

My goal remains the same. In order to succeed, I need to draw a card that matches the suit I name.

The addition of a single unknown factor introduces uncertainty. This is the purpose of the burn in competitive card games like poker, as well.

Now, there exist a number of possibilities:

• This unknown card is a spade, making my odds of drawing a spade 2/3

• This unknown card is a heart, making my odds of drawing a heart 2/3

• This unknown card is a club or diamond, making my odds of drawing either a heart or a diamond 1/3

During this specific call, it makes no sense to call any suit besides heart or spade. The odds of the suit coming up clubs or diamonds can never be more than 1/3. But there's no way of knowing what that other card is, at least right now. I just have to make a call.

This is the core of the two-deck game. I choose hearts.

I draw the Ten of Diamonds, and fail

The two-deck game is the resolution method I've built for a TTRPG that I'm currently developing. The goal of the two-deck game is not to necessarily make success harder as the game progresses, but rather to make success less sure. The goal is to build the feeling of insecurity in the players, to a greater degree than simply rolling a die.

The failure of a die roll in this scenario is that it makes the odds to clear. If I want a challenging roll and I know the odds are 1/20, the tension has now plateaued. I know the odds, and now all I can do is roll and hope.

With the two-deck game, I will always feel like I could have done better, even though there's no logical way I could've known what the hidden card was.

The two-deck game also creates a lot of interesting mechanical twists, where the goal of the players shifts away from improving all of their skills infinitely, and towards reducing uncertainty in any way possible. The easiest way is of course to just draw the unknown card, thus making it known, but what if each playbook has different narrative move that allow them to look at their deck, reorder it, or even remove cards from it? This ties together the emotions of the player with the emotions of the character, and creates ludonarrative parity: your character's goal of reducing uncertainty in the outcome of their action mirrors your player's goal of reducing uncertainty in their draw.

Later into the game, my deck has 6 known cards and 4 unknown cards

Here's another interesting thought: there's more than one way to call a card from a deck. For the purposes of this example, let's use some common RPG trait checks: "Mental", "Physical", "Charismatic".

• Each time I want to succeed at something mental, I need to name the correct suit. Originally these odds are 1/4.

• Each time I want to succeed at something physical, I need to name the correct color (red or black). Originally these odds are 1/2.

• Each time I want to succeed at something charismatic, I need to name Face or Number (with aces counting as a number). Originally these odds are 3/13.

With the two-deck game, we have some level of control over what cards are in our deck. Instead of deciding ahead of time that I'm going to be the strongest character ever, I'll let it build naturally over time. If I tend to use physical actions more often, I'll build my deck to focus on matching colors. In doing so, I will probably not be focusing as much on getting all face cards, or getting all the same suit. If I ever do need to make one of those checks (and I will, eventually), I will probably struggle with it immensely. This once again ties the abilities of the character to the abilities of the actual mechanic the player is engaging with.

4 Sample sub-decks. Known cards (red backs) are shown face-up, for ease of understanding

The two-deck game creates a lot of interesting possibility space that I'm currently working on exploring. Here are some other assorted thoughts:

• Tying the progress of the session to the size of the central deck. When the deck runs out, the session ends.

• Having players play different card games against each other at certain times using their decks to simulate PvP interactions.

• Giving unique moves to different playbooks, encouraging them to build their decks in slightly different ways.

• Changing the core moves partway through a session, forcing players to adapt with a sub-optimal deck and encouraging failure.

• Giving playbooks unique narrative elements related to the deck, that don't connect to moves at all: what if a character who's an oracle can draw a card from their deck and check a table to see a prophecy?

• Having major game moments tied to individual card draws: What if every time the ace of spades is drawn, a player character dies?

• Having different ways of adding known cards into each player's sub-deck, connecting the mechanics closer to the narrative.

• Adding or removing jokers, for any number of reasons.

Obviously not all of these ideas are good, and not all of these ideas will make it into the final draft, but they are interesting ways of expanding the functionality and use cases of the two-deck game, and making extra use of the levels of uncertainty it creates.

While this TTRPG is still in its relatively early stages, now that the core mechanic has settled down somewhat it will likely begin to grow quickly. Keep an eye on the design diary, and you might see more insight into its development!

-------------------------------------------------------------------------------------------------------

Playing card images were created by Byron Knoll, and can be found at https://code.google.com/archive/p/vector-playing-cards/