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Code algorithms that can take over the role of players from repetitious tasks.

Some games, especially online games, require players to perform smaller or larger sequences of actions repetitiously. One way to let players avoid this is through letting them relinquish control to a program, a Mule, for parts of the gameplay. While this may let them escape boring sequences of gameplay, if they are allowed to also create these Mules they are provided with a possibility of being inventive and creative.


The first possibilities to creates Mules appeared in Multiuser Dungeons. While DragonMud provided a limited way to add more content, Kingdoms made a programming language similar to C available to trusted players. The commercial massively multiplayer game Ultima Online provided similar but more restricted functionality through macros[1]. This was followed in World of Warcraft, which provides players with a set of functions that can be used for writing scripts. These scripts can vary from being practical macros that reduce the amount of excise but can also be more complex scrips capable of interacting with the environment.[2].

Although not created by the players themselves, the bots that can take over their role in the Left 4 Dead series can be seen as a form of Mules. This since they can let players take pauses during less important sections of them game.

Using the pattern

Agents Avatars Algorithmic Agents Proxy Players

Creative Control

Meta Games

AI Players

Diegetic Aspects

Interface Aspects

Narrative Aspects



Can Instantiate

Can Modulate

Algorithmic Agents

Can Be Instantiated By

Can Be Modulated By

Possible Closure Effects

Potentially Conflicting With


A revised version of the pattern Mule that was part of the original collection in the book Patterns in Game Design[3].


  1. Entry about creating macros on the UOGuide site.
  2. Entry describing the World of Warcraft API on the WoWWiki.
  3. Björk, S. & Holopainen, J. (2004) Patterns in Game Design. Charles River Media. ISBN1-58450-354-8.


Karl-Petter Åkesson