Okay, this cheat is really easy. All you have to do is go to the first Mine Cart Racing level and have Donkey first. Go until you get to the first crashed mine cart. Don't jump over it and crash. When Diddy jumps up and starts blinking push A+Y+left or right. If you do it right you will jump on air!!!!! To move in a direction push A and Y again and the direction you want to go in.The only way to beat the level with this is by falling back in the cart you came out of. If you go in a cart at the end of the level you will go to the very end of the level but crash into the wall and get stuck there. If this happens push START and while the game is paused push SELECT. It will make you exit out of any level if you get stuck in it.
Extras: You can also do this with Donkey. When you do it with Diddy you can jump up high and press Y and nothing else and he will do a flip.