Core Mechanics

During play, most of the actions in an RPG consist of the player designating a character to attempt some particular activity. The player must then roll dice (in video games, the computer simulates this) to determine how successful the attempt was. The rules governing success and failure for a particular activity describe how to test the die roll against one or more of the character attributes.

For example, consider the following situation: Johnny Rock, the warrior, wants to smash down a door. He has a strength of 17, and rules state that he must roll three six-sided dice and add their values. If he rolls higher than his strength, he fails to break the door. If he rolls lower than or equal to his strength, then the door splinters to pieces. Computerized games use more sophisticated versions of the same approach.

This play mechanic forms the basis of all the combat and most other activities in the game as well. As the character’s attributes go up, the probability that a character will be successful at a given activity improves. Complex calculations determine whether a character hits or misses an enemy, and if he does hit, how much damage he does. This can take into account a wide variety of factors: the type of attack; the levels of the attacker and defender; the amount of armor the defender is wearing; and so on. Because character growth is a key element of all RPGs, their core mechanics are designed around the character attributes.

Rolling Dice

Adding dice together is a pretty good way of generating random numbers in role-playing games. It means that most of the time a player will get a middling die roll, and only rarely will she get an extremely good die roll or an extremely bad one. However, as a designer you must understand the probability distributions of the possible die rolls when you’re assigning difficulty levels to tasks in the game because those chances are not evenly distributed. The chance of rolling an 18 with three six-sided dice is less than one-half of 1 percent. If you specify that a task requires a die roll of 18, it will almost never happen. On the other hand, if you specify that it requires a die roll of less than 18, it will almost certainly happen—over 99.5 percent of the time. Know your probabilities!

Character Attributes

There isn’t space in this book to give any more than a general introduction to implementing characters in CRPGs. If you haven’t played any kind of role-playing game before, take a look at the Dungeons & Dragons Player’s Handbook (Wizards RPG Team, 2008) for an introduction to how one particular game system describes and designs characters. Although character attributes vary from game to game, many games borrow from, and sometimes expand upon, those in Dungeons & Dragons because they are the oldest and most players are familiar with them.

In the book Fundamentals of Game Design, Third Edition (Chapter 9, “Creative and Expressive Play,” section “Self-Defining Play”) divides attributes into functional attributes and cosmetic attributes and further subdivides the functional attributes into characterization attributes and status attributes. We’ll look into these next.

Characterization Attributes

Characterization attributes determine the general abilities and qualities of a character and change only infrequently; status attributes describe the current state of a character and may change often. Choose attributes for your game based on the actions that you want characters to be able to take. The attributes will determine whether the character can in fact perform those actions and, if so, how well, how quickly, how powerfully, and with what probability of success. For instance, in the Dungeons & Dragons system, the dexterity attribute determines how likely it is that a character will be able to pick someone’s pocket without detection.

Here is a brief overview of some particular types of characterization attributes that you may wish to consider:

• Race is an unfortunate misnomer, as most games (rightly) do not distinguish among the conventional human racial classifications (Caucasian, Native American, South Asian, and so on) except as a cosmetic attribute. In RPGs, race refers to groups of real and fantasy humanoids such as humans, dwarves, elves, giants, and so on. A better term would be species, but race is the term established by convention. Attributes connected with race usually govern the general body type and appearance of a character; they may also imply limits on the upper bounds of his strength or other physical attributes. Some games limit particular races’ ability to perform certain types of activities.

• Sex naturally determines a character’s body type and may determine with whom the character may form romantic relationships, if the game includes them. (Many games assume that all their characters are heterosexual; Mass Effect is an unusual departure in this regard.) Otherwise, sex is almost always a cosmetic attribute rather than a functional one.

• Character class is a form of specialization that permits the character to perform certain actions (for instance, the Spellcaster class may perform magic spells), gain particular skills, and improve certain attributes while limiting the growth of others. The object is to encourage, or even require, the player to create specialized rather than generalized characters. This in turn compels the player to set up a balanced party containing a mixture of character classes, which is an additional challenge. Effectively, a character’s class determines his role in the party. Typical classes include fighters, spellcasters, thieves (with special stealth abilities), and clerics (with special healing abilities). You can undoubtedly think of others.

While character class is a traditional feature of tabletop RPGs, it is not essential, and it sometimes produces absurdities, such as a wizard whose class restrictions prevent him from using a kitchen knife. Not all games use character classes. If you want to implement classes, it would be better to define them in terms of limits on a character’s ability to improve certain skills rather than absolute prohibitions on certain activities.

• Physical attributes such as height, weight, strength, dexterity, endurance, maximum speed, maximum health, and so on determine how a character performs while moving, carrying weight, and during combat. Armor class is a commonly used physical attribute that contributes to the formula that determines whether a character will be hit by an enemy attack; it is roughly equivalent to defensive dodging in war games.

• Mental attributes such as intelligence and sanity affect the character’s ability to learn or reason and to withstand disturbing or horrifying situations. Because a player may be more (or less) intelligent than his character is, it’s difficult to enforce intelligence except by fiat. Some game systems use intelligence levels to place limits on the ability to cast certain kinds of magic spells.

• Moral attributes determine the character’s attitudes toward justice and exploiting others; in simple terms, the extent to which he is good or evil. It might be worthwhile to design a more subtle system of morality, however. Some people who think nothing of stealing wouldn’t dream of abusing an animal—and vice versa.

• Social attributes determine a character’s social attitudes and ability to get along with others. Examples might be charismatic, nurturing, or leadership abilities. You might also use social attributes to describe such things as a character’s degree of xenophobia or his conversational skill. When a character engages in conversations, you can design the dialogue engine so that it does not give an inarticulate character as many things to say as a more articulate character.

Some games—for example, in the case of the Fallout series—allow the player to establish the values of a primary set of characterization attributes, then calculate the values of a second set based on those in the primary set. In Fallout 3 (and its predecessors), the primary set of attributes includes strength, perception, endurance, charisma, agility, intelligence, and luck. The secondary set of attributes includes hit points (that is, maximum possible health, calculated from strength and endurance), armor class (based on agility), and so on. The Fallout series has particularly well-designed core mechanics.

Status Attributes, Experience, and Character Levels

In CRPGs, a character’s status attributes typically identify the character’s location, health, state of needs (like a need for food or rest), relationships with other characters, inventory of items owned or carried, and any other value that may change from moment to moment.

Among the most commonly implemented status attributes are two related ones that effectively measure the character’s growth: experience points, often abbreviated XP, and character level. Experience points are earned by successfully defeating enemies in combat and by other activities that the designer feels represent important achievements in the context of the game’s story. Usually these consist of completing quests or conducting successful negotiations with NPCs via dialogue. In a tabletop RPG, XP are awarded by the game master; in a CRPG, they are awarded by the computer when it detects a particular event.

Typically, XP have no intrinsic value and cannot be traded for anything else; they are simply a measure of progress, almost like a score. However, when a character achieves a certain level of XP, the character’s level goes up a notch. The amount required to reach a new level gets higher as the game goes on, because the player earns more XP for defeating more dangerous enemies. The thresholds are sometimes determined by the character’s class. Achieving a new character level (called leveling up) usually gives the player an opportunity to raise one or more of his characterization attributes. In many games, the player earns a certain number of points, often two or three, that he can add to whichever characterization attributes he is most interested in improving. Some parts of the game are often blocked until the player achieves a certain level in order to prevent him from wandering into an area that is too dangerous for him, and special features (such as the ability to ride a horse) are unlocked at particular levels as well.

If you implement character classes with different thresholds for leveling up, you should make this clear to the player before he has to commit himself to a given class.

Cosmetic Attributes

Because part of the appeal of role-playing is the ability to play as a character of one’s own design, CRPGs often have a great many cosmetic attributes. They add variety but don’t influence the gameplay. Cosmetic attributes include such things as hair, skin, and eye color; facial features and body shapes within a particular race; clothing and jewelry that doesn’t function as armor or have magic powers; tattoos, piercings, and other body modifications; and talismans, pets, or other distinctive objects that a person might keep nearby, such as Indiana Jones’s hat. In online role-playing games, rare examples of such objects are highly sought after and command high prices within the game economy, even if they serve no function in the game’s combat challenges. Cosmetic attributes add richness to the play experience; the more of them that you can afford, the better—although they are not a substitute for good gameplay.

Magic and Its Equivalents

Magic is such a distinctive aspect of role-playing games that we’ll look at it in a separate section. Note that for magic you can substitute psychic powers, spiritual power, mental energy, or any other concept that allows characters to influence the world, themselves, or other characters, by means not available to us in real life. Science fiction games often posit advanced technology that is, as Arthur C. Clarke observed, indistinguishable from magic. It may be characterized as technological, but it’s just as imaginary as magic is, so we include it here.

The use of magic is commonly restricted to a particular class of characters, often called mages, magic-users, or spellcasters. The purpose of this arrangement is to establish complementary classes of characters—one that is good at conventional physical combat and one that is good at magical combat, which encourages the players to create mixed parties containing members of both classes.

In tabletop RPGs, where it’s up to the GM to decide what is and isn’t possible, players can imagine all kinds of interesting things to do with magic. Unfortunately CRPGs are limited by the fact that the software has to know how to implement any spell—and of course players expect a visible manifestation of the spell as well, which means creating animation and sound to go with it. Magic is most often used as a weapon or a shield, and as a means of temporarily improving the values of the party characters’ attributes and harming the attributes of enemies.

Because magic doesn’t exist in the real world, you can’t assume that your player will know how it works in your game world. If you include magic in your game, you must define what kinds of things magic does and how to invoke it. Typically, when a spellcaster uses magic, he does so in a particular instance called casting a spell, the effects of which are usually immediate. (Few spells in games take time to begin working.) Some spells are over and done with right away, more or less corresponding to a shot in a strategy game; others may have a lasting effect that ends after a certain amount of time. The effects of magic spells are almost never permanent in games. Permanent changes are too significant to happen frequently, so any permanent change is normally made by the leveling-up process.

You must also create a way to limit the amount of magic available, just as characters must have limited strength and health. Dungeons & Dragons uses a rather awkward system for placing limits on magic, requiring a character to “memorize” spells that, once cast, disappear from the character’s “memory” in the same way that a gun consumes ammunition. The character must have time to rest and rememorize the spells before she can use them again. This was convenient in tabletop games where the players had to keep track of their spells by hand. Now that computers can do the bookkeeping, however, most designers prefer another system in which each spell consumes a certain amount of magical power, or mana, when it is cast. A character’s definition includes a status attribute for the amount of mana the character has at the moment and a characterization attribute for the maximum amount that she may have. Drinking magic potions or simply waiting for time to pass may restore the mana. This system permits the character to cast any combination of spells that she knows, as often as she likes, until her mana is gone.

Skills and Special Capabilities

In addition to the basic human-like characteristics—strength, intelligence, beauty, and so on—most RPGs let characters use and improve special skills and capabilities. CRPGs allow the player’s character to learn new skills over time, a rarity in other genres. The best-designed games allow the player to attempt to learn as many skills as she wants, restricted only by the time available, though her character’s aptitude in that skill will be based on previously assigned characterization attributes. You may want to allow characters to specialize, especially if the character practices a set of interrelated skills, while unpracticed skills gradually decline. For example, learning one skill, basic carpentry, could provide a solid basis for developing another, such as constructing buildings, whereas learning basic gardening would not.

Obtaining New Skills

Skills are somewhat analogous to the unit upgrades of strategy games; like unit upgrades, they allow a character to do something that he could not do before or to do it more effectively. The unit upgrade process in a strategy game is typically called research, whereas in a CRPG, acquisition of a skill is called learning. Characters often get better at a skill the more they use it, and they learn new things they can do with it (recipes for making things, for example). Sometimes a new skill (or the right to choose a new skill) is simply granted as a reward for having achieved a certain amount of experience. However, you can also require the player to seek out a mentor NPC who will teach the new skill to the character in exchange for money—similar to the cost of research in strategy games.

The analogy between skills in CRPGs and unit upgrades in strategy games is not exact, however, for the following reasons:

• In CRPGs, a skill earned by a character is permanent and stays with that character as long as he lives (and usually survives reincarnation as well). In strategy games, a unit upgrade ordinarily lasts only for the duration of the current mission or level.

• In a strategy game, an upgrade normally applies to all units of a given type, or sometimes to the player’s entire army and economic system. In a CRPG, a new skill applies to exactly one character—the one who learned the skill. It’s the difference between an industrial and a personal advance. CRPG skills are individual, like the ability to play music, rather than industrial, like an improved engine. Each character has to have his own record of skills learned to date.

• CRPG skill upgrades usually happen instantly, whereas research in a strategy game normally takes time. Although instant learning is completely unrealistic for something like archery or playing music, nobody wants to sit and watch while her character practices. Strategy game research doesn’t have this problem because research happens parallel to other activities.

Using Skill Trees

Skills are usually organized into a skill tree, a growth path analogous to the tech tree often found in other games. As with tech trees, learning a particular skill in the tree makes subsequent, more advanced skills available. Other than that and the differences in the previous section, they’re really quite similar.

Figure 6 illustrates the idea of skill trees as implemented in Diablo II. The right side of the screen shows a skill tree, one of three different trees for a single character, an Amazon. The tree currently shown is labeled “Passive and Magic Skills.” (The other two available for this character are “Javelin and Spear Skills” and “Bow and Crossbow Skills.”) Each icon represents a skill that may be learned, with the ones that are required first at the top (this tree is upside down). The arrows leading from icon to icon show the progression. An unlearned skill appears in dark grey, such as the horned helmet at the lower left of the tree. Skills that have been learned are shown in white.

Figure 6 One of the skill trees for the Amazon character in Diablo II (right side)

Players earn skill points in Diablo II through experience, and may learn a new skill or improve an existing one by assigning the skill points to one of the skills in the tree. The “Skill Choices Remaining” box at the upper right indicates that the player has two skill points available to assign to one of the skills. The small boxes next to each icon hold the number of skill points for that skill so far; each additional point strengthens the effect of the skill during play.

Character Design

The design of tabletop RPGs allows the player to create her own avatar character before the game begins. Most CRPGs follow this model, particularly multiplayer online RPGs. Sometimes single-player CRPGs allow the player to create not only an avatar character but all the members of the party. Others let the player create only the avatar, then add further, predefined characters to the party as the player encounters them in the game world.

Typically, players set their cosmetic attributes any way they like: name, gender, hair color, clothing, and so on. They can also choose their character’s race, class, and moral attributes if the game implements such features. For other characterization attributes, the usual mechanism is to allow the players to roll simulated dice to generate a number of points and then allow them to distribute the points among their attributes however they see fit. This lets them concentrate their points in whichever attribute they’re most interested in developing. Players are sometimes allowed to ask for a new die roll if the first one is too low. Recently, CRPGs have begun to abandon the random factor and simply give the player a fixed number of points to distribute among his attributes.