Midair P Speed Shell Bump Jump
Jumping on a falling shell midair and then immediately hitting it again to get up higher.
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First attain P speed. Jump at the very edge of the ledge and hold down Y and B. You will be landing on the shell after the peak arc of the jump. When you see the shell, release both Y and B right before you come into contact with it to get the first jump. As soon as you land on it hit hold Y and B again to get the second jump off the shell. If you do not let go of Y when you come into contact with the shell, you will grab instead of hit it. If you do not let go of B, you will jump off the shell and start heading back upwards. This can also be done while holding a Key, Spring, or P switch. The only difference is you never let go of Y and B.