To endow game characters with more realistic affective behavior, the notion of prospect-based emotions plays an important role: recent literature suggests that emotional states of such agents should not only be triggered by present stimuli, but also by anticipation on future stimuli, and evaluation of past stimuli in the context of these anticipations. Within the current study, an extension of the belief-desire-intention (BDI) model with prospect-based emotions is proposed, and is evaluated with respect to its capabilities of enhancing believability of game characters. The model has been implemented in the modeling language LEADSTO. In addition, a game application has been developed, in which a user can play a two games (tic-tac-toe and a game of dice) against an agent that is equipped with the emotion-based model. An empirical evaluation indicates that the model significantly enhances the agent's believability, in particular concerning its involvement in the situation. © 2013 IEEE.