In the downhill jam when you start out first of all you'll fast speed and then as you go down the hill there is a ramp right next to the rails that go over that pit. Go on the ramp at max speed and do a kickflip to indy into you heard me into the wall. If you did it right you should have stuck to the wall and you can do unlimited tricks, but it is impossible to land the trick and eventually you probably press too many buttons at once and fall off.
First press start and hold L and press down, right, up, right, up, left, and c-left on your controller pad the screen will shake telling you the code worked.
For fewer grind falls press C-up, left, C-down C-down, up, down, right; this will help you make fewer falls while you grind.
To Get Slow Motion press down, down, up-C, right-C, Left
This will help you get your balance evn though it's slow.
Start Location C-left, C-right, C-down, up, down
This is on made at the menu screen and will give you location to restart at.