Preheat your oven to 350°F (175°C).
Prepare the cake mix according to package instructions using water, vegetable oil, and eggs.
Pour the batter into a greased 9x13-inch baking pan.
Bake for 25 to 30 minutes or until a toothpick comes out clean when inserted in the center.
Remove the cake from the oven and let it cool in the pan for 10 minutes.
Poke holes in the cake using the end of a wooden spoon, spaced about 2 inches apart.
In a bowl, combine the chocolate fudge pudding mix and milk, whisking until smooth and thickened.
Pour the pudding mixture evenly over the cake, filling the holes.
Chill the cake in the refrigerator for at least 2 hours to set.
Top the cooled cake with whipped cream and sprinkle with chocolate shavings or sprinkles.