Game competition has promising potential to be a powerful pedagogical strategy. To maximize the benefits and alleviate its possible negative effects, a substitutive competition design is proposed in this paper. The substitutive competition is a kind of mirror competition, a competition of pet-styled virtual characters that represent learners' open learner models. An animal companion system, named My-Pet system, was implemented to realize such concept. A preliminary system evaluation was also conducted in an elementary school to examine the effect of the substitutive competition in the My-Pet system. The results revealed that the substitutive competition was helpful to students' increased motivation and time-on-task that further contributed to improved learning efficiency.