While Transitional Interfaces (TIs) have primarily been studied in stationary settings, recent advances in commercial technologies, such as head-mounted displays and smartphones, have made Mobile Transitional Interfaces (MobTIs) accessible to consumers. MobTIs differ from their stationary counterparts by providing users the ability to leave their tracking space and adapt to their surroundings. However, MobTIs also present challenges that require attention. The paper identifies three prominent challenges: the discoverability of MobTI content in the real world, the benefit-cost ratio of transitions, and the selection of appropriate input modalities.