On Whomp's Fortress, in the Shoot into the wild blue mission, from the starting point, go climb the tree to the left. An owl will fly out. Jump off the tree and grab onto the owl. Now, watch your map. Jump off of the owl when you're over the body of shallow water. Go get in the cannon next to it. Aim twoards the pillar on the bottom ledge in the back left side. But, when you are aiming twoards it, aim up, almost above the top ledge. If you aimed correctly, you will fly to the bottom ledge and smack into the far piller, stopping you from falling off. Turn around, grab the pole, slide down, and you have the star.