Preheat oven to 350ºF.
In a large mixing bowl, add flour, cocoa powder, sugar, baking powder, baking soda, and salt. Stir until well-blended.
Add eggs, vanilla, oil, and milk. Beat until smooth and uniform.
Add boiling water. Beat again.
Fill cupcake liners ⅔ full with batter.
Bake for 25 minutes or until toothpick comes out clean. Allow cupcakes to cool completely.
To prepare frosting, in a medium mixing bowl, cream butter and powdered sugar together.
Add 2 tablespoons of milk and vanilla. Beat well.
If it is too thick, add more milk. If it is too thin, add more powdered sugar.
Transfer frosting to piping bag or resealable bag and cut the corner off.
Using the edible pen, draw eyes and mouths on marshmallows.
Using a small amount of frosting, secure orange sprinkles on marshmallows for the noses.
Pipe frosting onto cupcakes.
Add pretzels, M&Ms, and decorated marshmallows.