Action Games - Fundamentals of Game Design - page 407

often can't be hurt by normal methods; damaging them may require special weap-
ons, a special attack method, or special timing. For example, the Piranha Plants in
Super Mario Sunshine are invincible until they open their mouths.

The boss character's appearance and actions complement the theme of the set of
levels it guards. Sometimes the boss character is simply a much larger version of
another character that the player already defeated. This enhances the gameplay by
allowing the player to predict some of the boss's behavior and gives him a small
advantage in knowing what to expect.

Games with a serious storyline aren't suited for such an unsubtle set of themed
levels, but even so, the themed level and big boss are mainstays of action games.
Virtually every level-based, action-based game today uses a succession of levels
increasing in difficulty, culminating in a climactic defeat of a big boss.

WILDCARD ENEMIES
To break up the predictabilit y of predefined waves of enemies, many games insert a
randomly generated wildcard enemy to provide a fresh challenge. Wildcard ene-
mies, unlike level bosses, normally attack at the same time as normal enemies and
behave in unexpected ways.

The Atari game Asteroids , for instance, offers predictable waves of enemies (in this
case drifting rocks; although they do not shoot, they are still an active danger), but
at random times during the waves, a UFO appears and follows an unpredictable
path, shooting at the player. The game awards extra points for shooting the UFO,
but trying to do this tends to distract the player and cause her to make mistakes: a
perfect example of risk and reward in an action game.

TIP Don't use spawn
points or monster
generators in single-
player combat games
set in realistic situa-
tions such as World
War II. In a realistic
environment, the play-
er reasonably expects
that when he clears a
region of enemies, it
will remain empty. You
can still have enemies
walk, drive, or fly in
from elsewhere, but
having them materialize
out of thin air destroys
your game's credibility.

MONSTER GENERATORS AND SPAWN POINTS
Many action games include a feature that causes new enemies to suddenly appear
in the game world. If the enemies appear from a visible object that the player can
destroy, that object is a monster generator . If the enemies appear seemingly out of
thin air at a particular location, that location is a spawn point . The game Doom uses
spawn points: Monsters suddenly appear, each in a flash of green light, and there is
nothing a player can do to prevent it. In Gauntlet , on the other hand, monster gen-
erators are machines visible in the game world. If the player destroys a monster
generator, no more monsters come out of it. As a result, the player has a choice of
strategies: fight the monsters or destroy the generator. The strategy with the lowest
risk involves destroying the monster generators before they can spawn too many
monsters, but players aiming for the highest score may delay destroying the mon-
ster generator until they boost their scores sufficiently by killing enough monsters.
This choice makes the game more interesting.

Monster generators and spawn points may create either a limited or an unlimited
number of enemies. If you design a spawn point that produces an unlimited