We present a mobile avatar system designed to provide a constant user-avatar interface for health behavior change therapy. The presented Android application replaces the user's phone background with an animated avatar. The avatar's level of physical activity is made to match the physical activity level of the user. This activity level is inferred using a decision-tree-based frequency analysis of the built-in phone accelerometers. User physical activity data collected is also sent via a mobile analytics platform (Countly) to be stored in a server. Also included in our demo is a simple website which pulls information from this server and places a user's avatar among other people's avatars. In this display a user can see how their avatar's physical activity compares to others', and observe their real-life physical activity behavior directly impacting the performance of their avatar in the virtual world.