I'm not requesting code, just a place to get directed or an explanation on what's required would be good enough.
To start, when the player is in the ball, you'll need to turn the PlatformStand bool to true in the humanoid. Then, you will need to weld a large ball onto (preferably) their HumanoidRootPart. For the movement , you should look up some basic tutorials an custom movement. I'm sure you can figure that part out. :)
-Crystal