Governments increasingly deploy transformative policy missions to accelerate industrial decarbonisation, combining ambitious climate targets with large-scale funding and coordination. Yet the roles of incumbent firms responsible for most current emissions remain underexplored in both research and policy design. This paper investigates how Sweden's 20 largest industrial emitters respond to the country's legally binding net-zero by 2045 target, focusing on their participation in the Industry Leap and Climate Leap programmes. Using a mixed-methods approach that integrates emissions statistics, project-level funding data, and social network analysis, we analyse firms' emissions profiles, decarbonisation ambitions, mitigation pathways, scope of action, collaborations, and engagement with mission-oriented policy instruments. We find that declared ambition levels are a poor indicator of active engagement, as several firms with very ambitious targets show limited participation, while medium-ambition actors emerge as central project participants. Our analysis identifies four strategic roles, transformative frontrunners, system enablers, adaptive followers, and peripheral bystanders, that capture the diversity of incumbents' responses. These findings move beyond binary leader–laggard framings and highlight the need for policy instruments that reward concrete engagement, foster collaborative infrastructures, and tailor support to heterogeneous roles in order to align incumbent behaviour with long-term mission objectives.