For the funnel cake: Whisk together the pancake mix with as much water as is instructed for 2 cups of dry mix in a large bowl. Stir in the sugar, graham cracker crumbs and just a tad more water to make the batter slightly runnier than pancake batter. Rest batter for 10 minutes.
For the cream: Beat the marshmallow cream, heavy cream and vanilla together in a large bowl with an electric mixer until smooth and easy to drizzle. Refrigerate until needed.
Add 1 inch oil to a large pan with straight sides and bring the oil to 365 degrees F. Line a plate with a paper towel.
Transfer batter to a funnel, snipped plastic bag or squeeze bottle and carefully pour batter into the pan in circling motions, overlapping a bit to create structure. (If using a funnel, control the flow by ladling the batter into the funnel and holding your finger over the tip as necessary.) Fry until golden on the bottom, about 30 seconds, then flip and cook just a bit more. Remove to lined plate.
Drizzle the cream over the top of the funnel cake and finish by using a knife or peeler to shave chocolate over the top. Sprinkle with graham cracker crumbs.