FUNDAMENTALS OF GAME DESIGN, SECOND EDITION
Core Mechanics Features
The core mechanics of action games should be simple and obvious. Action games have small numbers of resources, and the relationships among these resources are
straightforward: Being hit by an enemy costs energy points; collecting gold stars increases the final score; and so on. The player in an action game is too busy to study a complex internal economy.
Designers usually allow the player's avatar a small number of reprieves from death. The number of lives provided usually ranges between three and five. Colliding with an enemy or some other dangerous object costs the player a life. Players earn extra lives by picking up a powerup or reaching a certain score. The player's avatar is usually invulnerable for a few seconds when he reappears after losing a life, so he can regain his bearings. When the player loses all his lives, he must either start over or return to the most recent checkpoint or saved game. The limited-life mechanic remains standard for arcade games, but it is being replaced rapidly in console and computer games by designs that allow unlimited lives.
The player's avatar begins the game with a limited amount of energy, sometimes characterized as hit points or health. Dangerous encounters with enemies or other hazardous features of the game world deplete this energy; in some games time itself, just living in the game world, consumes energy.
This energy can often be partially or even fully replenished by using a collectible or a powerup, but when the avatar's energy is fully depleted, it dies. In a game in which avatars have multiple lives, when the avatar's energy is completely depleted, one of its lives is lost.
In some games, an avatar's energy is shared over a number of physical features —for example, energy can be a limited resource that is distributed between shields and fuel, requiring the player to carefully balance resources.
As a reward for progress, the player may be given a powerup, that is, the opportunity to increase her avatar's strength or some other attribute temporarily or even permanently. In the case of a shooter, this can come in the form of stronger weapons or shields.
A permanent powerup is one that remains with the avatar for an extended period— possibly the remainder of the game but at least the current life or level. Space Tripper (and many other shooters) uses this model, although Space Tripper is unusual in that when the avatar dies, it loses only powerups gained on the most recent level.
Temporary powerups provide a powerful but short-lived advantage. These may be limited by time—for example, the avatar may move faster, but only for a short period, from a few seconds to a few minutes—or by the number of times they can be used. For example, a shield may be used up after it has absorbed a certain
number of hits. A general design rule is that the more powerful the advantage, the shorter the time the avatar should be allowed to use it. The Quad Damage powerup in Quake III provides a perfect example of the temporary powerup; it quadruples the damage that the player's weapons do for 30 seconds.
Some games vary the use of powerups by using power points. The player receives a certain number of power points to spend on an upgrade and enjoys some latitude in deciding how she wants to upgrade her avatar. Space Tripper provides two main weapons; the currently selected weapon will be upgraded when the player uses her power points. Playing Space Tripper successfully requires that the player balance the upgrade points between these weapons.
Collectibles are bonus objects the player can pick up that are not essential to the game and are often used only to augment the player's score. The player is not penalized for failing to collect them, but if he can justify the risk, then the rewards are high.
Collectibles can also unlock secret levels or cause special bonus events to occur. In Rainbow Islands, the player can collapse rainbows onto his enemies. As the enemies die, they deposit crystals the player can collect to earn bonus points. Collecting the crystals in the right order (red, orange, yellow, green, blue, indigo, violet) opens a doorway to a secret level, which gives the player a huge score and a permanent secret powerup.
Many games employ a timer that counts down from some initial value to zero. When the timer reaches zero, some major game event occurs.
A level timer indicates how much time the player has to complete the level; if he fails to do so, the level and the level timer are reset, and the player has to start again. This is often accompanied by a life loss. If the player finishes the level with time remaining on the level timer, then this excess time may be multiplied by a constant as a score bonus, or the player may receive some other reward for completing the level early.
You can also use a timer to count down to a catastrophe. The player must achieve some task before the timer runs out, or the task becomes much more difficult to achieve. Sinistar uses this form of time limit to good effect; when the timer runs out, the eponymous Sinistar has been built, and the player is in a lot of trouble.
Time limits may also govern the effectiveness of powerups. In this case, when the timer runs out, a temporary powerup stops being effective, and the player's avatar reverts to its normal state. Pac-Man's power pellets, which allow the Pac-Man to eat the ghosts for a limited time, are good examples of this use of time limits.
For many action game players, earning a high score is more important than the story. Keep track of the player's accomplishments: completing tasks, defeating enemies, collecting items, length of time through each level, and so on. One of these numbers is normally more important than the others, especially if it is the one that determines victory over other players in a multiplayer game. Which achievement is most important depends on the subgenre of the game; in deathmatch shooter games, for example, frags (enemy kills) are the most important. Display the player's primary score, whichever score that is, onscreen at all times in the primary game - play mode. Display the player's other achievements at the end of the levels. Be sure to provide one or more high-score tables so the players can see their own earlier achievements in single-player games and compare themselves with others in multiplayer ones.
Many games reward skillful play with bonus scores and multipliers. The classic example of the score multiplier can be found in Pac-Man: After getting the power pill, the first ghost that the player eats earns 200 points, the next earns 400 points, then 800, and then 1600.
