Make cake as directed on box, pour mix into a 9x13 cake pan and bake as directed, just long enough so middle springs back when touched lightly (25 min. in the oven is perfect for us so it isn't overdone).
When done set on a cooling rack for about 15 min.
When cake is still warm poke holes all over so the holes go all the way thru to the bottom of the pan. Pour 24 oz of liquid chocolate sauce all over the sauce so it seeps in all the way to the bottom.
OR if you don't want to use chocolate sauce you can: In a bowl break up 6 HERSHEY'S Milk Chocolate bars into smaller pieces and microwave for 30 seconds, stir, microwave for 30 seconds, stir. It should be warm and nice and smooth without any chunks now.
Pour over your cake making sure the melted chocolate is poured directly over the holes so it can seep thru.
Put into the fridge for at least an hour, or until it is cooled.
Take out and spread your marshmallow fluff on top evenly.
Sprinkle your mini marshmallows on top of that.
Sprinkle your graham cracker crumbs.
Break up the remaining chocolate bar and push the pieces into the top layer of marshmallow gently so each piece that will be cut will include a HERSHEY'S square. Enjoy!