Action Games - Fundamentals of Game Design - page 410

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
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.
TIME LIMIT
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 complet-
ing 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.