Drawing upon the Stimulus-Organism-Response Theory and Flow Theory, this study aims to investigate the effects of environmental stimuli that are unique to the mobile multiplayer online battle arena (MOBA) environment (i.e., immediacy, social interaction, and competition) in inducing the state of flow, which is expected to be the basis of online game addiction and subjective happiness among the online mobile gamers. Besides, this study explores the uncharted role of addiction in suppressing the effect of flow on happiness through the theoretical lens of Rational Addiction Theory. The results indicate that all environmental stimuli are directly and positively related to the state of flow, which relates directly and positively to online game addiction and subjective happiness. Online game addiction is found to have a direct and negative association with subjective happiness, on top of its suppressor role that negatively mediates the relationship between flow and subjective happiness.