This achievement wants you to play one event with all of the heroes in the game. To buy all the heroes you need 13,000 credits. I suggest buying them after you have done with the World Tour first using Lars, since the best way to spend your credits is to unlock levels and proceed in the game. After you have bought all 4 heroes, just use every one of them to play the "Rotten Helmets" event. I suggest playing that event because there is only 3 races, and they are pretty easy (Race, Elimination & Checkpoint).