The Three Challenges

The real-time aspect of an action game increases the frequency at which the player has to evaluate some parameters of a situation, and then decide which ability to use.

Evaluate the distance

• Evaluate the distance to an enemy in order to choose which ability to perform
• Evaluate where your character will end up once the ability is performed

Because everything moves in real time

Evaluate the time

• Evaluate the time it takes to perform an ability
• Anticipate how much time your ability will last

Because everything evolves in time

Cleverness and anticipation

• Anticipate a combination of actions to perform in different situations
• Know which ability to use to counter the attack of an enemy

Because each ability is a tactical tool for the player

In parallel, there are many advantages to designing enemies which match the player's abilities. Indeed, one of the main purposes of adding enemies to a game is to create an interesting challenge to teach the player, little by little, the mechanics of the game.

An Enemy is a Challenge For the Player

When we have to design an AI behavior, a common tendency is to try to make the AI seem as clever as possible and feel human. For example, to create an immersive experience, we might want to have multiple enemies behave as a squad, or perform actions the player would interpret as clever ones.

However, we tend to forget that no matter how clever an AI enemy behaves, the challenge created by an enemy when the player encounters him is what will impact the game experience the most. This means that as designers we need to go back to what is fundamental in designing a challenge, and understand precisely what are the most important properties of an AI to offer the right challenge we are aiming for.

Define a precise challenge for each enemy. Because the main function of an enemy is to attack the player, and because most of the time the player can destroy the enemies, there are usually two important questions I ask myself when designing the behavior of an enemy:

• How can the player attack and destroy an enemy?
• How can the player defend himself against an enemy? 

Indeed, when we design an entire panel of enemies, we usually try to create very diverse ways to beat each of the enemies.Here are two examples from Spider-Man: Shattered Dimensions, to illustrate this point:

As shown by those schematics, the ninja and the kamikaze bomber each offer a different challenge to the player when he has to defend himself against them:

The best ability of the player to defend himself against the Ninja is the dodge ability.

The challenge of the player to defend himself against the Ninja is a timing challenge.

The best ability of the player to defend himself against the Kamikaze bomber is the web shot.

The challenge of the player to defend himself against the Kamikaze bomber is a distance evaluation challenge.

Challenge the Player's Abilities

As a complement to designing a different challenge for each enemy, it's also interesting to design the enemies with different values of weakness for each ability/weapon. In other words, it is interesting to design each weapon to be more or less efficient against each enemy.

- This pushes the player to use all the abilities he has?- This helps the player to learn the specifics of each weapon?- This also pushes the player to be tactical and to use the right ability at the right time.

To illustrate this point, here's an example analysis of weapon efficiency on the enemies in Halo:

Because of these properties, during a combat against multiple types of enemies the player might switch from one ability to another in order to be more efficient in battle.

Common enemy archetypes in action games

Since everyone is attempting to have enemies that match with the player's abilities, we often see the same kinds of enemies in many different action games. Indeed, there are a lot of advantages to use these common archetypes:

• they offer an easily understandable challenge
• they have a recognizable and dissimilar shape
• the player may already have an idea of how to deal with them without the need of a tutorial.

Here's a list of the the most common archetypes in action games, with the functionality they usually have in the game.

• Shield enemy: challenge the precision of the basic attack

• Heavy enemy: require a heavy attack to destroy

• Sniper: ranged attack to hit

• Bomber: close combat attack to counter