This paper reports on an empirical study that uses a Grounded Theory approach to investigate the creative practices of Machinima filmmakers. Machinima is a new digital film production technique that uses the 3D graphics and real time rendering capability of video game engines to create films. In contrast to practices used in traditional film production, we’ve found that Machinima filmmakers explore and evaluate ideas in real time. These filmmakers generate vague and underspecified mental images, which are then explored and refined using the real time rendering capabilities of game engines. The game engine assists the filmmaker to fill in indeterminate details, which allows creative exploration of scenes through playfully experimenting with parameters such as camera angle and position, lighting, and character position. Creative exploration distributes the cognitive task of evaluation between the human user and the Machinima tool to enable evaluation through exploring possible scene c...