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[xiyo1]

The whole thing stems from one simple problem
"The most complex mechanic that a strictly card-only game can have"
After coming up with a number of crazy mechanisms, I found the answer to this question far exceeded my expectations.
（I'm not sure it's appropriate to post on this board, this topic is about thinking and discussion of game design within the constraints of a particular environment. Maybe it will be a huge inspiration for those games with card elements, or maybe the idea isn't that interesting）

Anyway, it's a very complicated story, so I'll try to describe the idea as clearly as possible in the following part
1、The limitations that "pure card games" have
2、An example about a first-person horror card game idea

The limitations that "card-only games" have

 The concept of a card-only game is even stricter than a board game. There are many interesting board game today with very complex rules, but these rules could hardly exist directly in a card-only game.
card-only game requirements
1. The whole game can only consist of cards
This means that the game cannot have items like tablecloths, tokens, dice, etc. It must be a stack of cards.
2, All cards of the game must be treated as cards
For example, laying many cards on the table into one big map, or using cards as tokens to move or fight is not allowed. Cards can only be held in the player's hand or placed on the table in stacks. All players can do is look at the cards on top of the stack or put them to the bottom of the stack。

The benefit of these restrictions is that they make the entire game extremely portable. Players don't even need a table, they just need to pick up a stack of cards and read them like a book (it's kind of like playing a mobile game where you pick up a small piece of the screen to play the game)Of course, you can also turn any game under this rule into an easter egg or mini-game in other large games, because it is so small and simple that it does not require complex programming and lengthy tutorials

However, you may think that these restrictions are so strict that it is almost impossible for a game with complex mechanics to exist, but that is what this topic is about, and there are indeed some very interesting and complex rules

Let me suggest a very basic example to help understand this rule.
A galgame can easily run under this rule. You can read the cards in order to read the story and skip a specified number of cards when you make a choice. (I remember some novels designed this way, flipping to a specified number of pages when you make a decision)

Each stack of cards can store a state, and the top card can indicate how many cards need to be cut forward or backward to reach the next state under certain conditions. This is similar to a Turing machine, so logically the game under this rule can do a lot of things

An example about a first-person horror card game

These rules and restrictions were meant to make some simple games. However, once I come up with a first-person horror game under these rules, things started to get weird.

This first-person horror game consists of
1. A two-dimensional maze in which the player can move around
2. a monster that will chase the player
The path of the monster is not simply moving toward the player, the monster in the maze needs to find the correct path to the player, and even has its own patrol route when the player is far away.
3, the monster's movement occurs in places where the player cannot see. This means that players cannot play as monsters to chase themselves, but through a special mechanism that allows players to cut cards according to certain rules.
4, although the player can not see the movement of the monster, the player can always know whether the monster has been next to them or has caught them
5, of course, players can collect props, trigger the organ to change the maze and monster path, Compared to the crazy requirements above, these elements is much simpler but important as a part of the game


I was shocked when the game met all the requirements
It's really hard to imagine a game that can be so complex under such strict constraints.
And the design of the game stopped not because it reached the limits of the card-only game, but because it fulfilled all the requirements I could come up with. This means that the potential of the card-only game is still far from being reached.

I will describe in detail how the game meets all the requirements. And I'm not sure if any game already has a similar design. (Maybe card games are not suitable for first-person horror games, I haven't seen any similar designs although I've played a lot of board games)

（My writing skills are terrible so I'm not sure I can express this clearly. If this is really interesting I'd be willing to make a video to better illustrate）

1、2d maze
This is an important element to turning the game from a visual novel into a simple RPG game that can be operated. However, this solution is very easy to come up with

For a stack of cards, only the top card will be shown
Putting one or more of the top cards of a stack to the bottom will showing the cards after without changing the order of the stack.
Imagine that a stack of cards is a corridor. By continually placing cards from the top to the bottom, you are moving from the left side of the corridor to the right side. This is a one-dimensional maze.
If the stack is arranged like a two-dimensional array in memory, then moving a card is moving left and right, and moving a number of cards equal to the width of the two-dimensional array is moving up and down.
The barrier of the maze is the direction in which you cannot move. This information will be written on the cards, telling you which direction you can or can't move in the current position.

This is the form of a 2d maze, a stack of cards in a fixed order. The top card representing your position in the maze.
In the current design. The maze is 7*7, which means that moving one card is moving left and right, and moving 7 cards is moving up and down. There are 49 maze cards in total

2、Monster representation.
The order of the maze cards cannot be changed, which means that the monster cards cannot be together with the maze cards (otherwise they would become fixed)
The original version was designed in this way: The monster cards are a stack with the same number of cards as the maze stack. That means there are two stacks of maze cards, one indicating the player's position and one indicating the monster's position. This way players and monsters can move independently of each other.

3、How to control monsters.
The monster moves as same as the player. Moving one card is moving left and right, moving 7 cards is moving up and down. But where the monster should go can not be controlled by the player, but by something else.
Here comes the core of this game.
Monsters may chase players, patrol, and even have special action logic. The monster's behavior, no matter how complex, can be represented by a matrix. The rows of the matrix represent the player's position, the columns of the matrix represent the monster's position. The elements of the matrix represent the direction in which the monster should move under a particular combination of player position and monster position.
With a 7*7 map, the size of this control matrix is 49*49
Next, this matrix is somehow split into 49 copies and distributed over 49 player cards and 49 monster cards. The player can use the data on these two cards to calculate the direction in which the monster should move.
The solution given here is to split the whole large matrix into 49 smaller matrices on the player cards. Each matrix is a row of the original large matrix, representing how the monster should move in each of the 49 possible monster positions under that player location, and the monster card has the coordinates of the monster position.
Of course, in order to make the player can not see the movement of the monster. This matrix can be randomly disrupted so that the player cannot see the location of the monster directly.

4、How players know if they've been caught
In the current situation, the two stacks represent the player position and the monster position. The player can calculate the distance by subtracting the two coordinates to know whether he is caught or not. But this is obviously unacceptable. First of all this operation is very time-consuming. Secondly, if the player can know the monster coordinates, he can know the position and movement of the monster, which is not allowed

The solution is very simple. The monster stack cannot represent the absolute coordinates of the monster, but the relative coordinates of the monster to the player. The benefit of this change is very obvious. Whether the player is caught or not is written directly on top of the monster stack. And the information about the monster's proximity can be written on the monster cards as well. This does not affect the control matrix, because the monster movement is still controlled by the player position and the relative position. What is affected is that the range of monster relative coordinates is from -6 to 6. The number of monster cards becomes 169. This makes the monster card stack too thick.

To solve this problem, the relative coordinates must be circular. which means if the relative coordinates say that the monster is on the right of the player, while the player is on the far right of the map, the actual location of the monster should be on the left side of the map because the monster can't be outside the map. By this method, the number of monster cards changes back to 49.

As of this point, almost all of the requirements have been met. Other rules, such as triggering organs can be done by flipping the maze cards, which can change the shape of the maze and the way the monsters move. There can be some quests and stories. When players walk to a certain location they will meet NPC and talk to them. Some places can only pass once, some places can attract monsters to come, some places can avoid the monster chase. Finally, the player collects special props to run out of the maze or defeat the monster.

You can imagine how amazing the above games are driven by two stacks of cards. And this is far from the limit of card-only games. You will notice that this game doesn't even change the order of the stacks. However card-only games can allow changing the order of the cards, even moving cards from one stack to another. Based on these, I come up with a dungeon adventure game that can be played by multiple players, a kind of DND game that can be played without DM driven by stacks of cards held by each player. It is crazy.

Although there are some unavoidable problems with this horror game. For example, every time the player moves, he has to do multiple operations on the player stack and the monster stack (once to move the player stack, once to change relative position, once to move the monster stack), when the player moves around in the maze, these operations become very tedious. However, I think this game still has a lot of inspiration. It shows the power of programmability that a stack of cards can have. A lot of complex mechanics can be implemented only with a stack of cards.


(Not an advertisement, and I didn't really make this horror card game into real. I just thought this would be a really interesting idea)