I suppose this has been on here before, but here goes. I couldn't do the final Arena race in the shifter kart, my best was 2nd, but found a cheat. Start the race as normal, about 20 seconds in on your right there is a gap between the blue/white boards and the wall, you can just squeeze through that, turn right and over the finish line, do 8 laps like that and get gold. Easy peasy, lemon squeezy. Doesn't work on time trial, I am playing the anniversary edition of the game.