I wrote a tutorial at www.raywenderlich.com explaining how to do some basic mechanics of a card game with SpriteKit and Swift. I’ve played CCG’s for many, many years, and had a section on design and history that didn’t really fit in the article.
Design of Collectible Card Games
Collectible Card Games (CCGs) have been around in several forms for over 20 years. The Wikipedia entry gives a fairly thorough history of these games. At the core, CCGs involve a set of custom cards representing people, locations, abilities, events, etc. To play the game, the players must first select a subset of cards to build their deck, then players use their built decks to play the game. Decks tend to be built around a certain faction, creature type, or common abilities.
Every game is driven at some point by resources, such as gold, energy, mana, or honor. Some games have more than one resource type or divide a type into different schools, such as fire and air, or colors. How those resources are generated is one of the most important aspects of any game. Creatures and abilities have a resource cost, and this is one of the ways cards are balanced. In our example game, the resource is simply called energy. The most common mechanic is where cards themselves produce energy. Each energy card gives you access to one unit of energy. In building a deck, it is a responsibility of the player to include enough energy cards in their deck, or risk drawing a starting hand with cards to play, but no energy to pay for them.
Other resource schemes have a separate deck for resources, a faction card that starts in play and counts as a certain amount of energy, or a combination of the two. Different factions can even have different energy types, although this becomes difficult to balance.
In Magic: The Gathering, the resource is called mana, and is divided into five colors. Each color tends to have a certain type of ability tied to it. Players can mix colors freely, but the more different colors in your deck, the lower the odds of having the correct pair of mana and card to pull it off. In Legend of the Five Rings, players create two decks, one with abilities and combat actions, and one with gold-producing resources as well as characters, making the player choose between an early character and gold to play more powerful cards later in the game. Mage Wars has both a starting mana value, and a different amount generated each turn. Hearthstone uses a mechanic where each player gets one energy credit per turn. This approach takes the energy requirement out of the player’s hand, and provides a built in escalation. Each style of resource generation leads to different play styles, and has their own balance issues.
Make Decisions Meaningful
Good games have a meaningful tension to choices of action, such as risk vs. reward or short term vs. long term. If two different cards do similar things, one should not be always better than the other. If there is no reason to choose the weaker card, then remove it from the game, or add a restriction to the more powerful card. Energy cost, power, duration, restrictions, and side effects are all variables that can be tweaked to balance the two choices.
The simplest example of this trade off is in speed vs. power. In our example game, cheaper creatures can be played earlier and more often, but do less damage and have less health.
Phases vs. Freeform
Many CCGs have a turn structure where specific things happen sequentially in a turn. Reset cards, draw, discarding, buying, attacking, etc. In a tournament setting, for example, not drawing a card before you do other actions means you forfeit drawing a card that turn. As a designer, you get to choose how this is done in your game. One advantage of a digital game, however, is that the game itself can remind, or even perform these actions automatically. In the first version of the CCG example game, there were a draw, cast, and attack phases. You couldn’t summon creatures in the draw phase, etc. In the current version, the game draws a card for you at the beginning of the turn, and you can perform actions in any order. You can attack with one creature, cast another, and attack again.
The biggest factor in this decision should be the story of the game. In a showdown between two casters, it makes sense that the creatures would attack at different times. In Legend of the Five Rings, you represent a general of a powerful samurai family. The attack phase of this game is your army marching across terrain to attack another province. In this case it makes sense to have a single attack phase.
For some insight into the design process for Blizzard’s Hearthstone, take a look at this article at Polygon.