How to Get Mario Kart DS Stages Mirrored
- 1). Select "Retro Grand Prix" from the main menu. When asked to select kart engine size, select "150cc."
- 2). Complete the three cups, winning gold metals on every track. These cups are the Shell Cup, the Banana Cup, and the Leaf Cup. This will unlock the final cup in the Retro Grand Prix, the Lightning Cup.
- 3). Win gold metals on each of the tracks in the Lightning Cup. This unlocks Mirror Mode, which allows you to play through the entire Retro Grand Prix with mirrored tracks. For instance, instead of making the usual right turn after the start line at Moo Moo Farm, the turn will veer left.
Source...