In the past decades, video games have grown from a niche market to one of the major entertainment media, enticing millions of players worldwide. When ethical aspects of video games are being debated, the discussion oftentimes revolves around effects of their content, such as violence. This paper argues that effects of game mechanics, such as reward mechanisms, should be considered as well, as these are at the core of the appeal of games. We analyze the ethical dimension of behavioral game design present in Massively Multiplayer Online Role Playing Games (MMORPG’s). Using the framework of technological mediation, we show how opaque and seductive game mechanics can invite problematic usage patterns, such as excessive use with negative effects on well-being, and how designers can take responsibility for morally acceptable impact of their games. Having a practical focus, the paper concludes with several proposals for better design.@en