Action Replay is a device that can be used to hack Mario Kart DS and Mario Kart 7. It is the most common way to hack these two games, Mario Kart DS more commonly. By using an Action Replay, the player can do things such as play as shy guy, change R.O.B.'s color, give themselves 300cc, make themselves invicible and even play the test courses. Many YouTubers made videos about these codes. Two very popular YouTubers are Supastarrio and davidevgen.