Medimon is an educational role-playing game that integrates visual mnemonics, collectible creatures, disease states, treatment items, and artificial intelligence-powered non-player characters (AI-NPCs) to teach biomedical concepts. This single-arm mixed-methods feasibility pilot examined recruitment, gameplay uptake and progression, player experience, descriptive knowledge outcomes, and AI-NPC interactions during the Medimon endocrine level among high school students. Thirty students consented; 10 generated gameplay data, six completed paired 12-item pretests and posttests, and eight completed a PXI-style survey. Students played independently using a Steam-based build and encountered thyroid, pancreas, and adrenal educational content through exploration, quests, battles, and Medimon collection. Mean paired knowledge scores increased from 19.4% at pretest to 44.4% at posttest, although the change was not statistically significant in this small exploratory sample (p = 0.156). Audiovisual appeal, curiosity, and enjoyment were rated favorably, whereas Progress Feedback was the lowest-rated player-experience domain. Students who completed the posttest demonstrated greater gameplay duration, exploration, quest completion, and Medimon exposure than non-completers. Thematic analysis identified a mismatch between player expectations and AI-NPC scope, including fabricated quests, spatial directions, and game mechanics that introduced unreliable guidance into the educational environment. The study identified barriers related to gameplay uptake, progression feedback, posttest completion, and AI-NPC reliability that should be addressed before the educational efficacy of Medimon is evaluated in a larger controlled study.