This thesis examines Det stora älgspelet (The Great Moose Game), a mobile serious game developed in collaboration with SVT’s slow-TV program Den stora älgvandringen (The GreatMoose Migration). The study explores how authenticity—understood as the perceived reality mediated through television—is negotiated during the adaptation of a non-fiction broadcast into an interactive format. Using Harteveld’s Triadic Game Design (Reality, Meaning, Play) as the analytical framework, the research investigates how perceived authenticity influenced user engagement in a serious game.The findings show that authenticity in this project was not a fixed target but a dynamic balance among creative, editorial, and technical constraints. Survey data and telemetry suggest that engagement was shaped by factors such as age, gaming experience, and prior familiarity with the program. The study concludes that adapting slow-TV into game form requires negotiating between realism and playability; and that perceived authenticity, especially embedded in aparticipatory culture across media, increases user engagement.