"Serious Games [SGs] are applications combining educational content with gameplay by integrating learning objectives into a game-like environment" (Thillainathan & Leimeister, 2014, p. 1). However, they have not been used much in language teacher education and training (Ulicsak, 2010). This paper describes the design of "Creative Muscle," a SG and its use to train second language practitioners/ Master of Arts (MA) in Computer Assisted Language Learning (CALL) studentteachers in the use of Singularity Viewer Virtual World (VW) for online micro teaching. This game-based training was delivered in three one-hour sessions. Creative Muscle was based on creative writing as a metaphor. Data included the researchers' personal observations, screen recordings of students' participation, and the participants' reflective journal entries. The findings gave insights into the effectiveness of the use of the 3D SG as a VWs' training mechanism. Students' feedback further provided ideas for game improvement which indicated a good understanding of the game, and of VWs. [For the complete volume of short papers, see ED590612.]