The Sphero's ( www.gosphero.com ) diameter: 74 mm
Mars surface gravity: ~3.7 m/s^2
Marble Blast marble diameter: ~0.4 TU
Marble Blast gravity: 20 TU/s^2
The ratio is the same. I conclude that the marble is a Sphero, 1 TU = 18.5 cm, and MBG is set on a terraformed Mars.