This paper describes the effects of short-term practice with the custom-made 3D immersive videogame Octopus on arm-postural coordination in patients with traumatic brain injury (TBI). Unlike many other custom-designed virtual environments, Octopus includes an actual gaming component with a system of multiple rewards, making the game challenging, competitive, and fun. While standing, 6 individuals with mild-to-moderate manifestations of TBI practiced reaching and popping virtual bubbles with the left or right hand avatar. The bubbles, blown by the Octopus, followed a specific trajectory. Interception of the bubbles allowed flexible use of the postural segments (trunk and legs) for balance maintenance and arm transport. Participants practiced ten 90-s gaming trials during a single session, followed by a retention test. Whole-body kinematics was analyzed using principal component analysis. As a result of the short-term practice, the participants improved in game performance, arm movement time, and precision, mostly by adapting efficient arm-postural coordination strategies. Of the 6 participants, 5 showed an immediate increase in arm forward reach and single-leg stance time. These results support the feasibility of using the custom-made 3D game for retraining of arm-postural coordination disrupted as a result of TBI.