First go to Little-Big World near the top of the castle. (That's a door in the hall of images with a big star on it: there are two of those in the hall.) It's you jump into the little picture. You make your way up to the very, very top of little world, and ground-pound so that the water drains into a little hole. Then you go back down, and jump into the nearest pipe to go into big-world. Go all the way up to the very top, and fall into the hole where all the water drained into. That's where you will meet wiggler. You have to stomp on his head. And believe me, it isn't easy, especially when he's extra mad and runs around really fast! After you jump on poor Wiggler's head 3 times, he will give you a Power Star. To get under his house(that's where the red coins are), you have to change between little and big world a couple times to get down into a hole next to a narrow bridge above the place where the bird and Lakitu and Koopa and the sand is. Hope that helps!