FUNDAMENTALS OF GAME DESIGN, SECOND EDITION
Balancing Asymmetric Games
Asymmetric PvP games run a greater risk of suffering from dominant strategies because the players effectively play by different rules. In Fox and Geese, which Chapter 1 describes, one player controls a single fox on the game board while the other player controls 11 geese (see Figure 1.3). The fox may move in any direction and jump over the geese, while the geese may only move toward the fox. The victory condition for the fox is to jump over all the geese (removing them from the board), whereas the victory condition for the geese is to trap the fox so that it cannot move. Thus, the rules provide entirely different units, available actions, and victory conditions for each side. In designing an asymmetric game, you must test the mechanics for each type of competitor against every other possible type of competitor to make sure that none has a dominant strategy that confers an advantage over all his opponents. This lengthy and involved procedure makes it more likely that a mistake will get past the testers.
In addition to the risk of dominant strategies emerging, players often disagree on the fairness of an asymmetric game. It becomes much harder to judge whether a game really gives all players an equal chance of winning and doesn't disadvantage any player who plays by different rules or with different resources. These arguments often result in variants—alternative versions of the rules—which arise to rectify what players see as problems. Several variants of Fox and Geese have emerged: one that puts more geese on the board, one that includes two foxes instead of one, one that lets the geese move backward as well as forward, and so forth.
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You can balance a more complex asymmetric game than Fox and Geese by giving the players identical quantities of raw materials at the beginning of the game and then letting them choose what units to build using the raw materials. The Macintosh game Spectre allows players to design a tank by assigning points to three attributes: speed, armor (defensive strength), and shot power (offensive strength). Each player gets the same number of points, so none has a built-in advantage, but each can construct a tank that matches his own preferred style of play.
The point distribution system, while generally fair, doesn't absolutely guarantee that no dominant strategy will emerge. The risk always exists that one particular combination of features may be superior to any other combination. To help prevent this, the attributes to which the player can assign points should be orthogonally related. One attribute should not affect the domain of another attribute. Having two closely related attributes, such as health and armor, undermines the point system. The player should not be able to gain the same effect by pumping points into one attribute as she can by pumping the points into another.
Also, make sure that spending a point on one attribute magnifies the unit's power in that dimension to the same degree that it magnifies powers in other dimensions if the player spends that point on any other attributes. This means that, for example, if the player can spend 10 points on strength to double the unit's strength, spending 10 points on intelligence should not multiply the unit's intelligence by 1000. If using a point on intelligence produces a significantly greater chance of winning than using it on strength, a dominant strategy will emerge: Players will always put all their points into intelligence.
StarCraft offers the most well-balanced combination of asymmetric features in any war game available, which explains why, despite being over 10 years old, it remains a favorite at gaming tournaments. The game offers players a choice of three races called the Terrans (or humans), the Protoss, and the Zerg. Each race produces flying attack units, construction units, small infantry units, and so on. Most important, building these units carries approximately equivalent costs, in terms of raw materials needed: A Zerg, a Protoss, and a Terran each must use similar amounts of resources to build units that provide equivalent fighting power. The capabilities of the units, however, vary from race to race; therefore, the game is asymmetric. The Terran construction unit can repair damaged units, so assigning additional construction units to a job can speed repairs. Damaged Zerg units may heal themselves without a repair unit, but only at a fixed rate. Protoss units possess both health, which cannot be replaced by any means, and shields, which the Protoss may recharge at special locations. Because Protoss units possess both health and shields, they usually cost about twice as much as their counterparts in the other races.
StarCraft is an excellent example of a well-balanced asymmetric game, and well worth taking the time to study. Buy a strategy guide for the game and read about the attributes of the units. Notice how their costs tend to balance their abilities.
The balance in StarCraft makes use of both direct costs (computed from the amount of raw material required to build a unit) and shadow costs—hidden weaknesses.
