Unpredictable Behavior

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The ability of agents to make actions that are unexpected.

The rules and goals of games often make it possible to predict the behavior of agents in the game world to a certain extent, and learning to do so is often part of the enjoyment and challenge of mastering a game. However, in some cases it may be desirable to have unpredictability in agent behavior, either to make the game more challenging or to create more suspense. Agents that at least sometimes are difficult to know what they will do next have Unpredictable Behavior.


The ELIZA program can surprise people by seeming to follow human behavior in quickly changing subject or making strange connections. However, this is merely an artifact of a simple dialogue system that intentionally expresses itself vaguely so people need to read much into what it says for it to have any meaning.

Using the pattern

Unpredictable Behavior is a pattern for modifying how Agents behave. The easiest way to create the possibility for this is simply to let players control the agents but Game Masters can be more appropriate for Non-Player Characters.

Algorithmic Agents can be modified to exhibit this behavior also, in this case typically through Randomness but sufficiently complex rule-based behaviors can also produce this result as can vagueness which ELIZA shows.

While displaying previously unknown Abilities or Powers can be a form of Unpredictable Behavior, this is only the case for the first such events since after experiencing it players can assume that it might occur again.

Narration Aspects

Cut Scenes can be used to make Agents have Unpredictable Behavior for specific situations since the Agents do not need to abide to game rules during these events, but this is of course only unpredictable the first time players encounter the situation in which the Cut Scene took place.


The use of Unpredictable Behavior can give the illusion of Agents having Own Agendas which indirectly can support Thematic Consistency in Game Worlds. Rather obvious, Unpredictable Behavior can create Uncertainty of Outcome and Surprises, and thereby work against a game having Predictable Consequences.

When the Agents that have Unpredictable Behavior are players (e.g. through the use of AI Players or a Game System Player), this gives rise to both player Unpredictability and Performance Uncertainty.


Can Instantiate

Own Agenda, Surprises, Thematic Consistency, Uncertainty of Outcome

with AI Players or Game System Player

Player Unpredictability and Performance Uncertainty

Can Modulate

Agents, Algorithmic Agents, Non-Player Characters

Can Be Instantiated By

Cut Scenes, Game Masters, Players, Randomness

Can Be Modulated By


Possible Closure Effects


Potentially Conflicting With

Predictable Consequences


A rewrite of a pattern that was part of the original collection in the paper Gameplay Design Patterns for Believable Non-Player Characters[1].


  1. Lankoski, P. & Björk, S. (2007) Gameplay Design Patterns for Believable Non-Player Characters. Proceedings of DiGRA 2007.