This study aimed to identify and rank the serious game fidelity themes that should be considered for retaining both the learning potential and predicted market growth of serious games. The authors also investigated existing links between fidelity and AI. The methodology unraveled serious game fidelity through the co-development of a theory- and data-driven codebook, applying the constant comparison method for data analysis. The theory-driven codesstemmed from literature while the data-driven codes emerged from a heuristic user interface evaluation of a comic book style game, named ExMan. This article identifies five fidelity themes, with functional fidelity as most important, and postulates that functional fidelity is most suited to AI integration. This study delivers a fidelity-for-serious-games codebook and concludes that observing the suggested fidelity hierarchy could safeguard that neither digital game-based learning is watered down, nor the lustre of digital gameplay dulled. Furthermore, the authors hold that AI for serious games should be given a high design priority.