In a large mixing bowl filled with the cake mix, whisk in the pudding mix and ¾ cup of the crushed vanilla wafers.
Add in the water, oil, mashed bananas or chopped bananas, and eggs. Using a hand or stand mixer, mix on low speed until well incorporated.
Add batter into the paper liners in the muffin tins. Sprinkle a bit of the remaining crushed vanilla wafers on top. Bake for 18-20 mins. Allow to cool completely on wire racks before frosting.
In a large mixing bowl or stand mixer, cream the butter, and beat until light and fluffy. Slowly mix in the powdered sugar, vanilla, sweetened condensed milk mix for 1 minute or until creamy.
Prepare pastry bag and fill bag with frosting. Frost the cupcakes and then top with a bit of the crushed vanilla wafers. Garnish with one mini-vanilla wafer.
Serve and enjoy.