#1 - You can take a big shortcut if you jump across the river just after the first big turn. You need a mushroom or a star to do this (it is much harder if you use a star). Aim for the dark spot on the wall, if you do this right you can get towed up onto the big ramp.

#2 - In 150 cc you can jump to the left at the top of the big ramp and land on a bit of dirt near the finish line. If you do this right you will get towed to the finish line. This is very hard.