This paper is concerned with approaches to semi-autonomous avatars in virtual game worlds, and degrees of autonomy in relation to player-control. Approaches to semi-autonomous avatars can be divided into three groups based on the design goals of using them: relief, expression and impression. Players can be relieved of cognitive and operational load by for example automating the animations of body-language of avatars. Means of expression through body-language, types of actions performed, and reaction tendencies can express the nature of specific avatars to other players in the same world. Character-information available only to avatars' own players and personalised, subjective world-representations create individual impressions of worlds and avatars' parts in them. A shared aim of these approaches is to increase the believability of elements in the game worlds and the sense of presence and immersion for players. In this paper the prototype Pataphysic Institute is used to illustrate how expression and impression can be utilized by consideration of the implementation of possible characterising action potential of avatars.