Preheat oven to 350°F. Spray (1) 9x13-inch baking pan with nonstick cooking spray. Set aside.
Add cake mix to a large bowl. Remove 2 tablespoons of dry vanilla pudding mix from the package and set aside. Add the remaining pudding mix to the cake mix and stir to combine.
Remove half of crushed pineapple and reserve. Do not drain the pineapple. Add the remaining crushed pineapple to the cake mix along with the eggs and oil. Use an electric hand mixer to mix the batter on medium speed until completely combined.
Pour batter into the prepared baking pan and bake in preheated oven for 25-30 minutes or until a toothpick inserted into the center of the cake comes out clean.
Remove cake from the oven and allow to cool completely on a wire rack.
Once the cake has cooled completely, mix the Cool Whip and marshmallow fluff until thoroughly incorporated. Stir together the reserved pudding mix and reserved crushed pineapple and add this mixture to the Cool Whip mixture stirring until combined.
Spread the frosting on the cooled cake. Cover and refrigerate for at least 3 hours before serving.