The early stages of Mobile Serious Game (MSG) design are very complex. That is why many MSG research projects start with a brainstorming session, involving pedagogical and game experts. However, brainstorming with large groups of participants, who come from very different backgrounds, can prove to be long and inefficient. In addition, classic brainstorming techniques are not well adapted to the large number of constraints and technical limitations that need to be taken into account when designing MSGs (e.g. educational content, number of students, duration of field trip, fences). Our hypothesis is that the first stages of design can be efficiently supported by a board game. Indeed, games have proven to be very efficient to support collaboration and enhance motivation and they can be designed in such a way to encapsulate constraints in their game rules. In order to test this hypothesis, we created a meta-SG: a game for designing a botanical MSG for a natural park. The experimentation we conducted with 17 designers was very encouraging. The analysis of the videos, questionnaires and produced scenarios showed that the meta-SG generated a very lively and productive creativity session, and the constraints related to MSG design were not perceived as limitations but as challenging game rules. Designing Serious Games (SGs) for education is a complex process that involves several actors: SG experts, who have experience in using game mechanics to enhance learning, and educational experts, who master the didactics of the target pedagogical skills. The design of Mobile Serious Games (MSGs) requires a third type of actor, who masters the MSG's use context. This context is not limited to a set of measurable physical settings (Dourish 2004); it also contains domain specific notions that can only be identified by field experts who have a deep understanding of the physical context (e.g. location, boundaries, physical limitations) in which the MSG will take place. MSGs for museums, for example, need to be designed with a museum curator, in order to fit specific rooms and exhibits (Lonsdale 2005). Another important aspect to take into account when designing MSGs is the time context. For example, if a MSG is designed for a field trip, it must not last more than the time planned for this outing. We therefore adopt a design-based research method (Whang 2005), implying deep collaboration between our team of SG experts, pedagogical experts and field experts. Unfortunately, these experts have little time to offer for work sessions. As many before us, we were confronted to this problem during the ReVeRIES 1 research project. The goal of this project is to use mobile technologies to help humans recognize the trees that surround them, in a fun and motivating way. It involves SG experts, computer scientists, several botanists and botanical park managers. The main objective of our first creativity session was to help these experts collaborate, in order to produce plausible MSG scenarios, for the Echologia Park 2. These scenarios will be used as a basis to build an authoring tool for the park owners to create their own MSGs. We therefore needed to help the designers in producing a large number and variety of MSG scenarios, adapted to Echologia's constraints, and in particular to the park's morphology (e.g. fences, trees) and the park's visitor profiles (e.g. groups of teenagers, families). In the next section, we investigate the strengths and weakness of existing tools and methods for organizing such creativity sessions.