In a large bowl, pour 2-1/2 cups milk over 2 cups Berry Colossal Crunch cereal. Let set until cereal is soft, about 10 minutes.
Drain the cereal milk into a measuring cup. You should have at least 2 cups cereal milk, as some will absorb into the cereal as it softens. Discard the softened cereal.
Add the dry pudding mix to the large bowl. Whisk in the 2 cups cereal milk until smooth, about 2 minutes. Let pudding set for 5 minutes and then fold in 1 (8 ounce) container of thawed whipped topping until completely combined.
In a large serving bowl, begin layering the pudding. Place 1 cup Berry Colossal Crunch cereal into the bottom of the bowl. Cover the cereal with some of the banana slices. Pour 1/3 of the pudding mixture over the layer of sliced bananas. Repeat layers with 2 cups cereal, half of the remaining banana slices and half of the remaining pudding mixture. Repeat layers again, with 2 cups cereal, remaining banana slices and remaining pudding mixture. Dollop the other 8-ounce container of thawed whipped topping on top and sprinkle with remaining 1 cup cereal.
Serve immediately or refrigerate until ready to serve.