Preheat the oven to 350 degrees F. Line twenty-four 2 1/2-inch muffin cups with paper baking cups and set aside. In a large bowl, combine the chocolate milk, oil, eggs and the cake mix; beat with an electric mixer on low speed for 30 seconds. Using a rubber spatula, scrape down sides of the bowl and beat on medium speed for 2 minutes more. Spoon the batter into the prepared muffin cups, filling each two-thirds full.
Bake until a wooden pick inserted in the centers comes out clean, 18 to 24 minutes.
Remove from the muffin tins and cool on wire racks. For the marshmallow filling, in a large microwave-safe bowl, microwave the butter on high setting (100 percent power) for 20 seconds. Stir in the marshmallow creme. Microwave on medium setting (50 percent power) for 1 minute more. Cool for 2 minutes, and then beat with an electric mixer until smooth. Make a 1/2-inch slit in the bottom center of each cupcake. Spoon the marshmallow filling into a pastry bag fitted with a round tip. Pipe the filling into the slits in the cupcakes.
Place the chocolate chips in a medium microwave-safe bowl and set aside. In a small saucepan, combine the cream and corn syrup. Cook over medium heat just until boiling.
Pour over the chocolate chips and stir until completely smooth. If not completely smooth, microwave on medium setting (50 percent power) for 2 minutes. Cool until the mixture thickens, about 5 minutes. Dip the cupcake tops into the chocolate mixture. If necessary, use a knife to smooth the tops.
Place the cupcakes into another paper liner and let the chocolate harden a bit. Spoon the vanilla frosting into a pastry bag filled with a small round tip. Pipe a line of small loops across the center of each cupcake. Allow the chocolate mixture to set.
