Success in general chemistry requires active engagement with course material. COVID-19 accelerated the move to online courses, creating a crucial need for engaging course activities. The Mysterious Compound chemistry game was designed to engage undergraduate students in introductory chemistry concepts while allowing the instructor and students to assess students' confidence in course concepts. When comparing pre- and postsurveys, there were significant differences (p < 0.001) in students' confidence levels on all the topics included. Positive and negative feedback was elicited and analyzed through student surveys. This game is an easy-to-implement engagement tool due to its versatile online format and adaptable design.