Can somebody help me with the Grumble Volcano World Champion??

Do you mean doing the shortcut? It is not to easy to do and it might take a few tries. You just have to use the mushroom in the right spot. By the way, whats with the smiles?

To do the shortcut, you have to turn to the left near the finish line, so you're actually on the finish line, and aim at the lowest par of the mountain to your left (When you start) and then use a mushroom or two. It takes a few tries, as you have to be moving.

When on the mountain, you have to do the whole perimiter, as if you cut corners, it's not considered a lap.

I hate that cheat, it's hard to do.