Instructions
Find an area where there is a large bowl or two opposing walls where you can build up a lot of speed. You'll need to go back and forth between these two walls or sections of the bowl several times before you can try the 900.
Ride forward and once you've built up a sufficient amount of speed press "R2" to perform a spine transfer over the spine.
Press "Left," "Right" and "Circle" while in mid-air to perform a 900.