Preheat oven to 350°F (175°C). Grease a 9x13 inch baking pan.
Make cake according to box directions using eggs, oil, and water. Pour into prepared pan.
Bake for 30-35 minutes or until toothpick comes out clean.
While cake is still warm, poke holes all over using the handle of a wooden spoon.
Prepare pudding by whisking pudding mix with milk until smooth. Pour over warm cake, ensuring it fills the holes.
Refrigerate for 2 hours or until pudding is set.
Spread Cool Whip evenly over the cake.
Top with crushed Butterfinger pieces and drizzle with chocolate syrup.