After falling off your bike, hold L to remain on the ground.

Be The Cop- Z, C-Left, C-Down, C-Left, Z, L, R, C-Down.

Extra Bike- Use Big Game Mode to finish all the races to get 2 new bikes
capable of 300mph+

Insanely Fast Bikes- At the main screen put in Up, C-Left, C-Left,
C-Right, Left button,
Right button, C-Down, and Z.

The Mystery Level-Get at least 52 batteries and assault a cop 19 times in
the insanity level,stage 2. You'll hear a chime at main menu press c-up 
c-down(2x) z z R L L c-down c-right FAST. You won't hear a chime this time 
go to level 5 get 52 batteries in stage 5 and you'll get the code. Its tricky 
but you'll get it after the first 10 times, don't lose  patience.