Preheat the oven to 350 degrees Fahrenheit. Spray a 9x13 baking pan with nonstick spray.
Mix together the chocolate cake mix, eggs, oil, and water according to the cake mix directions.
Pour the cake batter into the prepared pan and bake according to the package directions, check to make sure it is done with a toothpick. A few crumbs are okay.
Let the cake cool for about 10 minutes.
Poke the cake all over the top with the end of a wooden spoon, or a fork.
Heat the hot fudge in the microwave until it is pourable, in 30 second increments. Pour the hot fudge over the top of the cake, and try to fill all the holes.
Pour the cherry pie filling over the top of the cake, and spread as evenly as you can.
Cover the cake with plastic wrap and put it in the fridge to cool for 1 to 2 hours.
Spread cool whip evenly over the top of the cake.
Chop a chocolate bar finely into chocolate shavings and sprinkle over the top of the cake.
Cover the cake and place it in the fridge to chill for another 2 hours, up to overnight.
Top cake with maraschino cherries, or fresh cherries, when ready to serve. Or top each slice with one as you're cutting it up.