MoDa is a web-based, agent-based modeling environment designed to help students represent complex scientific systems while learning programming. A key feature of MoDa is block unpacking, which allows students to open a high-level, domain-specific block, inspect its internal logic, and modify it while remaining in a block-based interface. This feature aims to maintain the accessibility of blocks while providing opportunities for more expressive modeling and deeper engagement with computing ideas. This demo introduces MoDa through a short guided experience in which participants build and adapt models of ecological phenomena. We highlight how unpacking supports the exploration, debugging, and extension of prebuilt blocks, enabling students to move beyond fixed primitives and reason about computational structures as they design and optimize models. Participants will engage with examples from a classroom study where high school students used unpacking to create diverse scientific representations. In addition, participants will leave with a clear understanding of how MoDa can be used to foster computing concepts and practices in interdisciplinary contexts, as well as practical ideas for integrating it into their own projects.