Preheat your oven to 350°F (175°C). In a large mixing bowl, combine the Devil's Food Chocolate Cake Mix with required ingredients as per package instructions. Pour batter into greased 9x13 inch pan and bake for 25-30 minutes, until toothpick comes out clean. Cool for about 10 minutes.

Using the handle of a wooden spoon, poke holes evenly across the top of the warm cake, about 1 inch apart.

In a microwave-safe bowl, combine sweetened condensed milk, semi-sweet chocolate chips, and heavy cream. Microwave in 30-second intervals, stirring until smooth, about 1-2 minutes. Pour ganache into holes and spread over top of the cake.

Refrigerate the cake for at least 1 hour to help ganache set.

Whip the heavy cream with powdered sugar until stiff peaks form. Fold in marshmallow fluff until fully incorporated.

Spread the marshmallow whipped topping over the cake, smoothing it out completely.

Melt additional chocolate chips with heavy cream in the microwave. Drizzle over the marshmallow topping.

Slice into squares and serve chilled.