Preheat the oven to 375 degrees F (190 degrees C). Coat 30 cupcake cups with butter and flour.
Mix flour, sugar, cocoa, baking soda, baking powder, and salt together in a large bowl. Beat milk, oil, eggs, and vanilla extract together in another large bowl; slowly add dry ingredients and mix well.
Spoon batter into the prepared muffin cups, filling each about 1/2 full.
Bake in the preheated oven until tops spring back when lightly pressed, 15 to 17 minutes. Take cupcakes out of tins and let cool completely, 10 to 15 minutes.
Meanwhile, combine confectioners' sugar, butter, shortening, milk, vanilla extract, and salt for filling together in a bowl; beat until well whipped. Reserve about 1 1/2 cups of filling mixture for decorating cupcakes. Add marshmallow creme to the rest of the filling. Fill a pastry bag fitted with a long, thin tip with the marshmallow mixture. Pipe into cooled cupcakes; let cream settle.
Mix confectioners' sugar, cocoa, butter, evaporated milk, and vanilla extract together for icing in a bowl until creamy. Mix in chocolate chips and corn syrup. Transfer to a microwave-safe bowl and microwave mixture on high for 30 seconds. Stir and repeat process until smooth.
Dip the tops of the cupcakes into the fudge icing and set aside to dry.
While icing is drying, place reserved filling for decorating into another pastry bag fitted with a writing tip. Decorate cupcakes as desired.