Generation Z presents unique challenges for serious games designers seeking behavioural change, expecting sophisticated digital interactions beyond traditional core mechanics. This paper introduces the Complementary Features Layer framework, integrating social, creative, and educational elements within transformational games targeting digital-native populations. We present empirical evidence from the MOB Tournament, a large-scale gamified mobility intervention engaging 2,560 Italian Gen Z participants over 10 weeks. The tournament incorporated three novel complementary features: (1) dynamic team formation with institutional matching, (2) user-generated storytelling through MOB Stories, and (3) educational integration via masterclasses and bonus questions. Dynamic team formation achieved 62.1% completion rates while preventing “ghost teams.” Educational integration demonstrated measurable knowledge acquisition with 67% accuracy across 2,266 responses. User-generated content sustained creative expression with 78 participants producing stories over 19 days. Phase 3 engagement recovery (12.39 trips per user per week) exceeded Phase 1 levels (10.95), demonstrating complementary features’ effectiveness in sustaining motivation. The tournament achieved 33.28% active participation and 6.86 tonnes of CO2 savings, providing scalable design principles for youth-focused sustainability interventions.