This glitch allows you to jump as high as you want and as many times as you want in a row. In oder to activate it, you first must know about the debug code for Wario that let's you edit your coin and hats.
The code : In order to to activate the code, pause your game in a level and pres select 16 times until a cursor appears, You can use the cursor and the D pad to change any values from lives to coins. In order to move the cursor, you must hold A+B. What isn't easy to see is that if you press up on the Wario icon to the left, you can switch to his next hat/make him big and small.
The glitch: While jumping and as you're holding the A button, pause and activate the code. Use it to change Wario's next hat on the icon . Hold A and unpause and you'll make an extra jump. At the height of the jump you can do it again.