Massive open online courses (MOOCs) have developed rapidly and become tremendously popular because of their plentiful gamification designs, such as reputation points, rewards, and goal setting. Although previous studies have mentioned a broad range of gamification designs that might influence MOOC learner engagement, most gamified MOOCs fail to meet learning objectives because of a lack of research regarding suitable game design, as well as poor rationale for or design of gamification mechanics. This study aims to explore and identify engaging gamification mechanics for MOOC learners. We conducted a focus group interview with 25 MOOC frequent users to identify 40 gamification mechanics. This study then determined the relative engagingness of these gamification mechanics by administering an online survey to 5,020 MOOC learners. The results indicated that the 10 most engaging gamification mechanics accounted for more than 50% of the engagingness. The mechanics of the Where's Wally game is extremely engaging for MOOC learners; however, it has not been demonstrated in previous relevant studies. Finally, we discuss the top five engaging gamification mechanics and their implications.