When designing a performance involving people and mobile robots, we must consider the required functions and shape of the robot. However, it can be difficult to account for all of the requirements. In this paper, we discuss a mobile robot in the shape of a ball that is used in theatrical performances. Such a spherical robot should be agile and be able to roll like a ball. However, it is difficult to create a robot with all of these characteristics. Instead, we propose a mobile robot that can give the audience the optical illusion of the unique movements of a sphere by mounting a spherical LED display on a high-agility wheeled robot. The results of an experiment using a prototype indicate that this sort of robot can broaden the range of possible performances by giving the optical illusion of being a rolling sphere.