Preheat oven to 350 and line muffin tins with liners. Place an Oreo in the bottom of each liner.
In the bowl of a mixer, combine cake mix, eggs, melted butter, and water. Mix on low speed for one minute. Increase speed to high and beat for a minute more. Fill liners 2/3 full and bake for about 20 minutes or until tops of cupcakes spring back when lightly touched.
While cupcakes cool, make your filling.
Prepare filling: In the bowl of your mixer, beat butter, vanilla and whipping cream on medium low speed. Add marshmallow cream and beat on medium until smooth. Slowly beat in powdered sugar until just barely mixed. Increase speed to high and beat for one minute, until fluffy. Frost cake and serve.
Once cupcakes are cooled completely, fill the cupcakes. You can do this by cutting a small hole in the top of the cupcake and spooning the filling in, or putting the filling in a pastry bag with a bismarck tip and piping it in through the top of the cupcake.
In the bowl of a mixer, beat butter, cream, and vanilla on medium-low until smooth and well-combined. Slowly add powdered sugar. Once powdered sugar is barely mixed in, increase speed to medium-high and beat for 2 minutes. Fold in crushed Oreos.
Generously frost or pipe frosting on cupcakes and top with a mini Oreo if desired.