Prepare and bake cake per directions in two 8" round pans. Let cool then slice each layer in half down the middle to create 4 layers.
Prepare chocolate pudding mix per directions, let chill. Place Butterfinger candy bars in a Ziploc and crush to create small chunks.
In a large dessert bowl, place 1st layer of cake, top with chocolate pudding and Cool Whip and sprinkle with Butterfinger candies. Repeat this for each layer to create 4 complete layers of cake and toppings. Chill and serve.