My Mom would always make this cake for us when we were young, for birthdays. We loved it. The devil's food/chocolate cake would chill just right with the bananas, pudding, and cool whip. It was a chilly gooey mess on your plate.
I fancied it up by putting it in a trifle bowl and using the best chocolate cake recipe I know, instead of a box mix. James really loves cake but he prefers his "plain". He wasn't sure what to think of the Mess Cake even though he loves each component individually. Silly kid.
You must serve this kind of cake in a bowl. You'll never get a perfect slice on a plate. Just put it in a bowl and swirl it all around so you get chocolate, banana, and cake goodness on each spoonful.
My baby sis Kiki makes a version with oreos. She's such a rebel.