Non-Player Characters

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Diegetic persons in game worlds that are not controlled by players.

Note: the use of characters in this pattern and the pattern named Characters differs. Here, the usage of character complies to the common usage in the gaming community of referring to the graphical representation of a person in the game world (a sort of non-player version of the Avatar patterns). Although the common usage may also often imply the presence of the Agents and Characters patterns, this is not necessary and not presumed when used here.

Note: the abbreviation NPCs is very common for Non-Player Characters and is used here as well.

Many games depict fictional worlds populated with people of more or less human qualities. Since rarely all of these are controlled by players, by necessity those not under player influence need to be Non-Player Characters. These can range from still dummies to highly advanced AI systems or puppets for game masters but all have in common that their fate and ability to influence the outcome of a game is not on the same level as that controlled by players.

Examples

Although not that interesting as personalities, early arcade games such as Pac-Man can be said to have NPCs since each of them was given some unique feature. Here the NPCs fill the role of adversaries and this can be done even if they are not directly presented in the game, since they can be implied through how they affect gameplay, e.g. by driving the other cars in the Need for Speed series.

Many games use NPCs for several different reasons - it is quite common to have some NPCs provide specific actions such as trading or giving quests and have other NPCs only be enemies. Examples of this include Torchlight, Super Mario series, The Legend of Zelda series, and the Thief series. CityVille and Empires & Allies have Non-Player Characters that are never encountered in the game worlds but only appear in popup windows and neighbor lists. Black & White series uses NPCs to provide mortal beings that can be caused to fear or idolize the player's god. An additional use of these NPCs is that they can provide a means for game world in single-player games to have a population, something which can also be used to increase the population of multiplayer games such as World of Warcraft and to avoid making it feel completely unpeopled.

The later instances in the Elder Scrolls and Fallout series have NPCs that have daily routines, go through the actions of eating and sleeping, and have short conversations with other NPCs. They also have allegiances to various social groups and will come to the defend of other members of these groups if they are attacked. The games in the Fable series function similarly. Although these NPCs have complex behavior, they are only on part of the gameplay in these games. In contrast, the interactive drama Façade focuses nearly entirely on interacting with the NPCs Grace and Trip, and observing how they interact with each other.

Sometimes the issues of whether a diegetic person is an NPC or not depends on the play mode, and can be mostly a subjective opinion. For example, when playing the Left 4 Dead series with other players it is quite clear that they are not NPCs but when playing one of these games alone offline they are more likely to be treated as NPCs. Playing alone online is more unclear since other players may join but one does not know that until after the fact (one could argue that the designers see them as NPCs in this case since the server shuts down if one disconnects). Although example of a borderline case is in the Sims series; any Sim in the active household can be controlled by a player but does not need to be, and Sims from other households created by the same player may come for a visit but do this as pure NPCs.

Using the pattern

Non-Player Characters are fundamentally diegetic Game Elements. Their most important characteristics are which role they play in relation to the players and the Game World they inhabit, and this can be modulated through their appearance and disappearance through Game Element Insertion and Game Element Removal. Since some NPCs mainly have roles as extras, in fact being Self-Service Kiosks that serve as Helpers, this somewhat paradoxically mean that it is not necessary for all Non-Player Characters to be Generic Adversaries or Characters. Instead, it may be more important that they can recognized during gameplay for what they are, which for NPCs that are supposed to individually distinguishable probably means that they need to have Diegetically Outstanding Features. The lack of Character does not mean that they cannot play essential parts of Narration Structures, they can perform these roles through Cutscenes. In fact, through the use of Cutscenes NPCs can be part of games even if they rarely or never can be perceived or interacted with in the actual Game World. One specific example of this is Browser in many of the Super Mario series, he is typically encountered early during gameplay and then several times throughout the game through Cutscenes but is only possible to interact with him as a Boss Monster during the final fight of the game.

A primary choice when designing NPCs is whether they should have agency within the Game World. Making them Agents is typically achieved through the use of Algorithmic Agents, Dedicated Game Facilitators, or Game Masters, but can sometimes be done through Spectators (especially in games with Pervasive Gameplay, e.g. Prosopopeia). An additional option to adjust the level of agency is to consider giving the NPCs Initiative, although this may lead to a loss of Predictable Consequences. When NPCs have agency, they can take the opposing roles of Enemies (and Boss Monsters) or supporting ones of Companions by giving them Preventing and Supporting Goals respectively. By using these options, Quests can easily be modified to provide Casual, Complex, or Challenging Gameplay. The role of Enemies can make it possible to allow activities requiring many participants, e.g. Races or King of the Hill competitions, in Single-Player Games although in contrast to Multiplayer Games this is typically done as part of some Meta Game where the player can improve Skills or Abilities. That being said, in many cases it is not necessary to consider the possible NPC aspects of Enemies - it is sufficient to simple see them as Enemies. One example of this is as opponents that make Evade goals more difficult; in this case the primary concerns is how the NPCs can move in the Game Worlds and perceived events that take place there. The use of Companions can be predetermined by Predetermined Story Structures, the Reward of successfully completing Gain Allies goals, or be possible to create as Player-Created Characters during the initial set-up of games. NPCs used as Companions can also affect Narration Structures by having Linked Destinies or being the cause of Internal Conflicts for players. The options players have in interacting with NPCs can through these means easily be made into Character Defining Actions.

Even without agency NPCs can provide many different types of opportunities for interaction with handling Trading of Transferable Items and the assignment and adjudication of Quests being common. Likewise, they can be important parts of goals through being the senders and receivers in Delivery goals, being the objectives of Guard, Rescue, or Guide and Protect goals, by making up the pool of possible candidates in Match-Making goals, or the receivers of Binding Promises to make Committed Goals diegetically present in the Game World. When the NPCs only can perform these actions (due to not having agency) they are in principle Helpers or Self-Service Kiosks for the players.

Providing NPCs through Characters is related to the choice of giving them agency but can be done independently and opens up for many design choices, e.g. providing them with Equipment. Characters without agency can provide Complex Gameplay but does so without forcing players to become reactive. ELIZA can be argued to be an example of this although this is achieved through a set of response rules rather than through abstract characteristics. Adventure games such as The Secret of Monkey Island series and the first instances in the Fallout series can also be said to do this, but through Dialogues in this case. NPCs which are Agents with Character typically provide even more Complex Gameplay, as for example found in the Sims series and later installments of the Elder Scrolls and Fallout series.

Being able to engage in Dialogues with NPCs is a common functionality. This may be as simple as a Canned Text Responses to show that they have nothing important to say (but makes finding NPCs with something to say a form of exploration goal) but can also be the primary type of interaction (as in, for example, ELIZA and Façade). Combining Chat Channels with Non-Player Characters does create a powerful medium for Dialogues but these are only as powerful as the parsing ability of the system and its ability to generate specific responses. Besides allowing Predetermined Story Structures to unfold, typically uses of Dialogues include: giving, supporting or finishing Quests or other Predefined Goals; providing services such as teaching Skills; or giving Gossip that either indicate Optional Goals or shows Memory of Important Events (e.g. Persistent Game World Changes). By making NPCs part of Main Quests game designs can guarantee that players will have encountered them if they have completed a game. For games supporting more Complex Gameplay through the use of Dialogues, the specific challenges of False Accusations or Brokering and the goal of Maintaining Lies are possible.

One of the uses of NPCs is to create Factions that players can interact with or become members of. The goal to Gain Allies can also be modified so that successfully completing it results in a whole Faction becomes an ally rather than a single NPC, and actions towards individual NPCs can easily become Character Defining Actions since they can affect a player possibilities to interact with a whole Faction. Individual NPCs can has special statuses in these Factions by being Social Gatekeepers, competitors in situations of Internal Rivalry, or by secretly being Traitors setup to commit Betrayal at some point. Having NPCs in Factions, or at least implicit ones through a willingness to talk to each other, make it possible to modify many of the gameplay possibilities of Dialogues to be possible through Eavesdropping (possibly requiring the completion of Stealth goals).

More generally, NPCs can be used to make the culture and social norms of Game Worlds part of the gameplay through Diegetic Social Norms. This make it possible that Actions Have Diegetically Social Consequences, e.g. assaulting people in civilized areas provoke attacks from the law authorities as in the Assassin's Creed or the Elder Scrolls series. While this can regulate which actions are not socially acceptable, and when, by the NPCs, Diegetic Social Maintenance can be used to make it socially unacceptable to not perform certain actions according to some rule set. All of these can be applied on both general levels and on Faction levels, creating more Complex Gameplay by making players need to handle competing and possible incompatible social rules.

Note that NPCs do not actually need to be able to perform actions that change the game state, and more specifically players do not have to able to interact with them at all. The core of NPCs are their role in a Narration Structure, and as such they can exist only as Diegetically Outstanding Features or only be seen through Cutscenes. One example of this can be found in the Massively Single-Player Online Games CityVille and Empires & Allies - here the Non-Player Characters are only seen in the HUD Interfaces of the games even though players can visit some of their Private Game Spaces.

Diegetic Aspects

Since Game Worlds typically should be populated with inhabitants, NPCs are in many cases required for them to have Thematic Consistency. The exception is when these inhabitants can be treated as one or several groups but without individual differences within the group(s) - in this case the use of Units suffice. Since Boss Monsters are supposed to be distinct from Enemies, NPCs can be a necessity in this case as well.

One design goal with NPCs can be that they should be believable as humans or self-aware individuals with the same emotional and social responses as those associated with humans. This can be rephrased as the goal of making players take an intentional stance towards the NPCs when anticipating their actions[1]. This may be an unreachable goal using current technology but temporary successes are possible (most famously shown already with the ELIZA program in the 1960s). The suggestions below provide options that designers can apply depending on how much effort they wish to put into placing people in an intentional stance and keeping them there.

A basic requirement for this to be possible is that the NPCs is in a Game World so that it has a space to act within (which may be the real world for games using Real World Gameplay Spaces). How they behave in this world needs to have Thematic Consistency for the NPC to fit there, and this may require Awareness of Surroundings, Context Dependent Reactions, and Memory of Important Events. The NPCs in the Fallout series partially exhibit these characteristics: they make comments about their surroundings and commonly known world events but ignore corpses in their immediate proximity.

A second basic requirement is that they are Agents. As mentioned earlier, this is typically done through Algorithmic Agents or Game Masters but can in some cases also be done through Spectators. Examples of ways to increase players impression of NPCs agency (in contrast to simply making them more powerful) includes providing them with Initiative, Own Agendas, Competing for Attention, Barge-In, and Unpredictable Behavior. The four first of these are present in the interactive drama Façade while the last one may result from the system's inability to parse player input - this does not necessary need to be a bad thing and is part of the reason why ELIZA works (in combination with using Ambiguous Responses). Others fortune affects own Mood is related both to having Thematic Consistency in response to what happens in the Game World and to having agency - it can be expressed through how Memory of Important Events are made visible or through attacking those that threaten others in one's Faction. For games striving for Replayability, it can be important to provide each NPC, or at least for the most important ones, with an Open Destiny to avoid risking that players take the NPCs experiences as predetermined and thereby not necessary to involve oneself in. Games using Generic Adversaries to create NPCs can for the discussed reason here want to make them at least have different appearances and possibly varied Characteristics even if they are Generic Adversaries.

Another aspect of NPCs Thematic Consistency is how player can interact with them. That one cannot interact in all the ways people can interact with each other in the real world is typically accepted just as one cannot perform all the actions possible in the real world. However, when there are inconsistencies in that one can perform certain actions towards some NPCs but not others problems can arise (the same goes when some NPCs can perform actions and others cannot but diegetically should be able to). For example, it is not possible to attack NPCs of your faction in World of Warcraft. Although this might be argued to be Enforced Agent Behavior to preserve the Thematic Consistency it can also be seen as limiting players' Freedom of Choice and limiting the Creative Control of players by making the Roleplaying of their Player-Created Characters difficult or impossible. However, allowing this can ruin Predetermined Story Structures and lead to Unpredictable Behavior in the eyes of other players. Another example of this is the inconsistency in the Fallout series regarding if it is possible to kill children or not. Besides the moral issues related to these types of design questions, typically trying to acknowledge these possible actions requires more resources in the development of game and may only be worthwhile if one if aiming to support Sandbox Gameplay. Having NPCs provide Loot is also related to their Thematic Consistency and can make them Resource Sources.

There is actually another, even more basic, aspect of making NPCs to have Thematic Consistency. This is that their representations should mimic their states as appropriate for the setting (a form of Diegetically Outstanding Features). In games like the Super Mario series this may be that the Bob-ombs Enemies flash and sound before exploding while in games with high granularity in their Combat system such as the Fallout series this may require Visual Body Damage and Dissectible Bodies. In games which simulate Sports, it might even be appropriate to let NPCs perform Ragequitting, Sid Meier's SimGolf is an example of this in that the NPCs opponents one is playing Golf against can give up and leave an ongoing game if their mood turns sour.

Tutorial Neighbors are a special kind of Non-Player Characters which have some characteristics of passive players. They are used as ersatz Neighbors in Massively Single-Player Online Games such as CityVille and Ravenwood Fair where they provide initial places for Visits and give players Quests.

Interface Aspects

The amount of interaction available with NPCs can easily become overwhelming. Although breaking Thematic Consistency, this is often solved through the use of Secondary Interface Screens to provide separate interfaces (and modes of play) for activities such as Dialogues and Trading of the allowed Transferable Items. The cost of this for Dialogues is making Barge-In more disruptive and Gameplay Integrated Conversations impossible.

Narrative Aspects

Many of the notes above regarding Quests and diegetic aspects are also strongly related to Narration Structures in games. This is quite natural since having people convey information or emotions is one of the most flexible ways to provide information and many stories revolve around social relations and - NPCs can be a way for designers to do both these things and typically so through Dialogues as well as preconstructing NPCs or events related to them as Predetermined Story Structures. For games basing their Narration Structures on a Detective Structure, this is especially likely to be useful since information to a player has to be provided to that player's Avatar or Character. The use of Game Element Insertion and Game Element Removal of NPCs can be powerful narrative devices besides their impact on gameplay.

Consequences

Since the creation of any NPC implies a Game World it consists in, have a NPC either requires a more fully developed Game World or creates one anyway but without Thematic Consistency. Further, since the core of NPCs is to present a diegetic person it is at odds with the Units patterns, both because NPCs typically have some individual variation and that they by definition are not controlled by players.

While giving NPCs Preventing Goals introduces Conflicts and possibly Combat in games, Cooperation and Team Combos can be achieved through giving them Supporting Goals instead. One example of this is that situations where players have Internal Rivalry with NPCs can lead to them having to engage in Puzzle Solving. Agency of any type in connection to NPCs automatically provide Enforced Agent Behavior and typically leads to Complex Gameplay (except when used in conjunction with Supporting Goals when it instead can provide Casual Gameplay). This complexity is typically multiplied by the level of detail put into the Character connected to each NPC, if any.

Relations

Can Instantiate

Binding Promises, Dedicated Game Facilitators, Delivery, Dialogues, Diegetic Social Norms, Diegetic Social Maintenance, Eavesdropping, Factions, Gain Allies, Gossip, Guard, Guide and Protect, Helpers, Internal Conflicts, Linked Destinies, Match-Making, Narration Structures, Predefined Goals, Predetermined Story Structures, Thematic Consistency, Trading, Quests

with Algorithmic Agents, Dedicated Game Facilitators, or Game Masters

Complex Gameplay, Enforced Agent Behavior

with Chat Channels

Dialogues

with Dialogues

Brokering, False Accusations, Maintaining Lies

with Enemies

Boss Monsters, Challenging Gameplay, King of the Hill, Races

with Internal Rivalry

Puzzle Solving

with Loot

Resource Sources

with Preventing Goals

Conflicts, Combat

with Supporting Goals

Casual Gameplay, Cooperation, Team Combos

Can Modulate

Challenging Gameplay, Game Worlds, Quests, Rescue, Skills

Can Be Instantiated By

Characters, Cutscenes, Diegetically Outstanding Features, Game Elements, Generic Adversaries, Self-Service Kiosks, Tutorial Neighbors

Can Be Modulated By

Agents, Actions Have Diegetically Social Consequences, Algorithmic Agents, Ambiguous Responses, Awareness of Surroundings, Barge-In, Betrayal, Character Defining Actions, Companions, Competing for Attention, Context Dependent Reactions, Cutscenes, Dialogues, Diegetically Outstanding Features, Dissectible Bodies, Enemies, Equipment, Game Element Insertion, Game Element Removal, Game Masters, Initiative, Internal Rivalry, Loot, Main Quests, Memory of Important Events, Open Destiny, Others fortune affects own Mood, Own Agenda, Player-Created Characters, Preventing Goals, Ragequitting, Secondary Interface Screens, Social Gatekeepers, Spectators, Supporting Goals, Traitors, Transferable Items, Unpredictable Behavior, Visual Body Damage

Possible Closure Effects

-

Potentially Conflicting With

Units

with Enforced Agent Behavior

Creative Control, Freedom of Choice

History

New pattern created in this wiki. However, most of the material is collected from earlier research papers [1] [2] [3] [4] [5].

References

  1. 1.0 1.1 Lankoski, P. & Björk, S. (2007). Gameplay Design Patterns for Believable Non-Player Characters. Paper presentation at DiGRA 2007, Tokyo, Japan.
  2. Lankoski, P. & Björk, S. (2007). Gameplay Design Patterns for Social Networks and Conflicts. Paper Presentation at Computer Game Design and Technology Workshop, John Moores University, Liverpool.
  3. Lankoski, P. & Björk, S. (2008). Character-Driven Game Design: Characters, Conflicts, and Gameplay. Paper presentation at GDTW, Sixth International Conference in Game Design and Technology, 2008.
  4. Brusk, J. & Björk, S. (2009). Gameplay Design Patterns for Game Dialogues. Paper presentation at DiGRA 2009: Breaking New Ground: Innovation in Games, Play, Practice and Theory. London, UK.
  5. Lankoski, P. (2010). Character-Driven Game Design - A Design Approach and Its Foundations in Character Engagement. D.A. thesis at Aalto University. Publication Series of the School of Art and Design A 101. ISBN 978-952-60-0002-2.