In Pianta Village on episode 6: Secret of the Village Underside when you have yoshi go to the main brown and green mushroom with the little green one (which is the first mushroom after you jump down from the starting platform) go to the pink mushroom on your left then go for the next brown and green mushroom and get close to the edge as you're landing and miss but stay on the tree as you go all the way down. If you get it right,you'll fall down beneath the world and be in a black zone where you can see clouds and blue up above you. Also you can see a Pianta under a tree as you look around.