In this feasibility study with a mixed methods, quasi-experimental design with a pre-test and post-test, we aimed to learn from an online game-based SEL intervention for vocational education students (12-16 years) how to develop and implement such non-linear interventions in schools. The SEL intervention TalentQuest+ started in October 2018 and lasted eight months. It consisted of a questionnaire that assigned them an archetype of a Greek god based on their results. Participants then chose challenges that helped them improve on the strengths and weaknesses of the archetype. The program was self-directed. Data of 66 students were analyzed. The number of challenges completed (132) suggests that students did not engage actively with the program. Self-reported open mindedness, self-efficacy, task performance, emotion regulation, and self-reflection were measured at baseline and post intervention, and did not increase significantly. However, qualitative data showed some metacognitive self-reflection skills in half of the students, who learned to think differently about themselves and about strengths and weaknesses. The study showed several implementation and design issues, including a lack of explicit guidance.