Line a cupcake pan with 12 paper cupcake liners, and set aside.
In a medium mixing bowl, mix together the graham cracker crumbs, sugar, and melted butter. Mix until entirely combined.
Evenly distribute the mixture into the cupcake liners. Firmly press into an even layer and set aside.
The Cupcakes
Preheat the oven to 350°F.
In a large mixing bowl, combine the flour, sugar, cocoa powder, baking soda, baking powder, and salt with a whisk. Then add the water, vegetable oil, and vanilla extract. Mix until completely combined. Add the eggs and mix just until combined.
Fill each cupcake liner about 2/3 of the way and bake for 18-20 minutes or until an inserted toothpick can come out clean. Place on a cooling rack and allow to cool completely before frosting.
Marshmallow Buttercream Frosting
In a large mixing bowl combine the softened butter, marshmallow creme, and vanilla extract with a hand mixer until smooth and fluffy.
Slowly add the powdered sugar with the mixer on medium speed until completely combined. Transfer to a piping bag and frost each cupcake.
If desired, top with graham cracker crumbs, a piece of chocolate, and a mini marshmallow.