On the second world, there is a level called “Millstone Mayhem”. Enter the level, playing with Diddy. Jump on the tire and go the right until you see the monster. Quickly go back down, jump on the tire and go to the left. You should land on the top of the doorway. When the monster comes down and walks to the doorway, you need to slide down and land on its head, holding Left. The longer you hold it, the more lives you should get.