The study of transmedia storytelling has in recent years turned towards a more historicized understanding of its object of study, and also shifted to a wider perspective on narrative and narrative elements, focusing more on the transmediality of story-worlds and world-building rather than just narratives (‘plots’) in the stricter sense. This article combines these interrelated perspectival shifts in an analysis of story-worlds/world-building in two transmedia franchises: The Shadow (1931–present) and Transformers (1984–present), with a focus on the mechanics and processes of world-building in relation to transmedial change (i.e. how world elements are transformed over time as well as when story-worlds move across media platforms).