As the name implies, MoYu Rainbow Ball (6.5cm) is a ball-shaped challenge. There are several circular holes all throughout the ball. All but one of the holes are filled with a smaller ball. Because the smaller balls may be put into the vacant hole as long as they are next to it, the Rainbow Ball functions similarly to a three-dimensional Klotski puzzle. Being able to utilize the ball as a puzzle and for play as a ball makes it much more entertaining.