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.