Preheat your oven to the temperature specified on the cake mix box, typically around 350°F (175°C). Grease a 9x13-inch baking pan.

In a large mixing bowl, combine the Devil's Food Chocolate Cake Mix with the eggs, water, and oil according to package instructions. Mix until smooth, about 2-3 minutes.

Pour the batter into the greased baking pan and bake for 25-30 minutes until done. Check with a toothpick.

Remove the cake from the oven and let it cool in the pan for about 5 minutes.

Using a wooden spoon handle, poke holes at 1-inch intervals all over the warm cake.

In a microwave-safe bowl, combine sweetened condensed milk, 1/3 cup heavy cream, and chocolate chips. Microwave until melted and smooth.

Pour the chocolate filling into the holes, spreading any remaining filling over the top.

Let the cake cool to room temperature for about 1 hour, then refrigerate for 2-3 hours.

Whip 1 1/2 cups of heavy cream until thick. Gradually add powdered sugar and vanilla extract, then fold in marshmallow fluff.

Spread marshmallow topping evenly over the chilled cake.

Melt 1/2 cup of chocolate chips with 3 tablespoons of heavy cream over low heat. Drizzle ganache over the topping.

Refrigerate the cake again for about 30 minutes before serving.