Sonic Riders: Zero Gravity Hints for Wii
Also on: PlayStation 2
SCR-HD:-Come first in a race with him in it on free race,best to do at the start of the game.
Nights:-Complete every mission
Amigo:-Complete every mission
Billy:-Complete every mission
I would do them all but I can't remember which story you have to complete but the good news is, is that these characters are hard too unlock!
Okay guys, here's the thing. You don't have to do anything to unlock this guy. In fact, you'd have a better chance of getting him WITHOUT unlocking anything. HD appears randomly throughout Free Races. If he appears, do whatever you can to get 1st Place so you can get him. However, he'll appear less often if there are unlocked characters taking his place. For best results, do Free Races RIGHT WHEN YOU START A NEW FILE. At the very beginning, only 7 racers will appear on the roster. That way, the 8th racer will either be GP or HD. Any course, any rules. Finding this flying robot is all a game of luck.
To win a race easily take advantage of every shortcut you can find and use.