Mega Mouse
From Sonic Retro
File:Megamouse.jpg
Sega Mega Mouse
American Version
This version came with a total of four (4) buttons: 'A', 'B', 'C', and 'Start', just like the standard 3-button Genesis/Megadrive control pad. This version came with a red-and-black mouse mat.
Other Regions
This version has a mere two buttons but it could be turned upside-down and the ball used as a trackball. If the ball is pressed in it acts as a button press. The European version came bundled with a blue mousemat.