To unlock this trophy, you need to win an online match with either: Backfire, Scarab or Zippy.
In the game, you are given weekly challenges, if you are lucky you will manage to collect one of these many cars in them. If you do, you just have to win one online match, it can be in either: Casual Duel, Casual Doubles, Casual Standard, Casual Chaos, Competitive Duel, Competitive Doubles, Competitive Standard, Rumble, Dropshot, Hoops, Snow Day, and possibly in online tournaments. An easy way also is to hit up your friend(s) and ask them if they can help you.