CAKE: Preheat oven to 350 degrees, grease and flour two or three 9-inch cake pans. In mixing bowl, combine cake mix, mandarin oranges with juice, eggs and oil. Beat for 2 minutes with an electric mixer. Pour into prepared pans (layers will be thin) and bake for 20 to 25 minutes or until a toothpick inserted into the center of the cake comes out clean. Remove from pans, allow to cool completely.
FROSTING: In a mixing bowl, combine pineapple with juice and vanilla pudding mix, fold in whip topping. Frost cake and refrigerate until ready to serve. Best served cold.
Cook's Note: There's enough frosting to frost the sides of the cake too. I just liked the way it looked here in the photo. You'll also need another can of mandarin oranges to decorate the top, if desired.