First collect the Turbo Nozzle on the island behind you (the "real" box is in an alcove in the grassy slopes, on the opposite side of the tower from you). Switch to the turbo nozzle, run at Piantissimo, and dive at his feet - the idea is to start close to him, but facing the flag. Charge the turbo as you cancel his speech bubble to begin the race, and blast off underneath the hut. Jump once to climb onto the next strate, and keep to the right of the mirror. Ahead of you is a gap in the side of the wall, which leads to a brick path on the upper tier. What you want to do is, from the sand, while turboing, spin jump onto the bricks. It's a big jump and there is not much room for error in the angle, so expect to crash into thing over and over.
−
Strat here
+
Assuming you make it from the sand to the bricks with a single turbo-spin-jump, push North-West on the joystick and do a tiny tap on the A button as soon as you touch the bricks. If done correctly, Mario will very briefly push against the grass on his left, and hop on it. If done incorrectly, you'll either not make it onto the bricks in the first place, or accidentally perform a triple jump. If things go according to plan, Mario will continue turboing up the grassy hill, straight to the flag and make it there in under 10 seconds. This takes him right to the finish flag, hopefully in under 10 seconds. Remember, you should be holding down the R button the entire time!
+
NB. It is possible to achieve a time under 10 seconds without the spin jump - you can stop turboing to perform a double-wall kick, and charge the turbo in mid air to relase it as you land onto the grassy hill.
+
+
NB. It is believed to be impossible to spin jump directly onto the grass from the sand. The bricks are slightly lower than the grass, so they are a suitable alternative and only a slight detour from the "straight path".