Conceptual, emotional, and political challenges are entangled in environmental issues, yet science education often focuses exclusively on the conceptual dimension. To address this, we developed a design workshop to study how high-school youth could integrate all three in their creations. Specifically, we explored how youth negotiated visions of thinking, feeling, and acting for sustainability when positioned as designers of embodied participatory simulation (PartSim) activities for younger students. Through an analysis of video, design artifacts, and youth's written reflections from a six-session workshop, we reveal how youth leveraged familiar genres of activity to invite and structure participation in their embodied PartSim activities. In particular, we analyze the design process of groups that drew on game conventions and iteratively designed their activities to foreground competitive and cooperative forms of participation. They used these participation structures to evoke configurations of thinking, feeling, and acting that contrasted guilt and regret for unsustainable actions with hope for collective action toward more sustainable ecosystems. We argue that designing for collective activities with the embodied PartSim infrastructure offered space for youth to explore the severity of environmental issues in serious yet playful ways that foregrounded a sense of hopeful responsibility.