Designing a combat system is a recurrent exercise many designers will have to do in their career. When I had to do this for the first time many years ago, I had a hard time. Not only was it hard to obtain good results in my designs, but it was also hard to find information which would explain the overall basic rules experienced combat designers use to achieve interesting combat mechanics.

With the help of other designers, I have decided to gather and formalize what knowledge I can on the fundamental rules in designing a combat system. This article is the result of that exercise.

The main objective we have in mind when we design the gameplay mechanics of a combat system is to push the player to make clever choices and use the right ability at the right time. We want the player to be able to anticipate the next action he'll perform and also to develop a tactical plan during the combat.

There are many ways to reach this result, but here are two very important characteristics which help to design the player's abilities for a combat system:

• Each ability has a unique function: hit a specific area, stun an enemy...
• Each ability is balanced with the reward vs. the risk of using it.

The Tactics of Abilities

With those characteristics in mind, here are some analytical examples of some classical abilities in a military shooter such as Call of Duty:

1. Each ability has a unique function

Another way to think about the design of these abilities is to consider each one as a tool for the player.

The following schematic presents a panel of abilities in Call of Duty, and the area affected by each of them:

• Melee attack. Covers an area in front of the player at close range. The player can only use it at close range, but it kills an enemy in one hit.

• Normal shot. This is the basic attack the player can use at any time. It is the optimal attack at middle range only.

• Iron sight shot. Perfect for performing a very precise shot to an enemy standing far away, e.g. a headshot. Very dangerous to use because of the loss of peripheral vision.

• Grenade. Perfect to hit enemies behind a cover or in a corner. It also kills enemies in one hit. But it's consumable, so the player must be careful to spend it at the right time.

Now imagine if every one of those abilities could be instantly performed by the player. We would achieve an interesting challenge, which is "press the right button at the right time".

But this isn't enough. As mentioned earlier, when we design a combat system, we are really aiming to challenge the cleverness of the player, and the tactics he'll be able to apply during the battle. So basically we want a system with multiple choices, but in which the player has to evaluate and choose the best option for each situation.

2. The tactical layer: the risk versus reward trade-off for each ability

Not only does each ability allow the player to attack a certain way, but they each have advantages and trade-offs. Here's a detailed example from Street Fighter II.

There are plenty of different types of advantages and trade-offs a designer can create for an ability. Here are some of the most commonly used ones in action games:

Advantages. Damage Output, Stun, Repel, Damage Over Time, Blindness, HP Regeneration

Trade-Offs. Consumable points, Cooldown, Time to Activate, Recovery Time

Even if each of these abilities is perfectly balanced between risk and reward, it is always good to offer the player a panel of abilities with different coefficients of risk vs. reward.

Some abilities of the player character will, for example, do small damage to enemies, but are not risky to use because they are quick. On the extreme opposite end, special attacks can do a lot of damage, but are often very risky to perform, due to startup or recovery times.

Each combat system offers a selection of abilities with different coefficients of risk vs. reward.

An ability is also a tool to counter the enemy. Keep in mind that sometimes abilities not only allow the player to attack enemies, but can also be used to counterattack them. Therefore if the player uses an ability at the wrong time, he could either miss an opportunity to hit an enemy or worse, he'll lose HP because he could not counter the enemy. This is why performing a counterattack is also part of the risk taken by the player when he performs an ability.