In this paper, we propose an authoring tool for creating mobile mixed reality games (MMRGs), referred to as M2RGC (Mobile Mixed Reality Game Creator). Goal is to transform the game creation process in a task that is as interesting as playing the game itself. Therefore we offer a user-friendly interface through which different MMRGs can be created by defining the objects used in the game, their behavior and interaction with sensors (e.g. GPS, compass). The tool itself uses the power of MPEG-4 BIFS[1] capabilities, such as the possibility of grouping multimedia assets in a scene. We build a wrapper over these MPEG-4 BIFS functionalities allowing anyone to discover the experience of MMRGs creation. Concerning the client runtime for playing the game on mobile phones, we deploy a MPEG-4 player on the Windows Mobile and Android platforms.