Preheat oven to 350 degrees. Mix packaged cake mix according to directions. place a regular size Oreo cookie in the bottom of each. Take 1/2 of remaining cookies and chop coarsely and add to cake mix. Fill the cupcake tins. Bake for 15 minutes (or according to box directions). While cupcakes are baking make the frosting.
Cream together butter and cream cheese. Add vanilla, then add powdered sugar slowly until blended well. Chop remaining regular-sized Oreos very fine (I put the cookies in the food processor instead of trying to chop them up super fine and it worked out really well). Add to frosting. After cupcakes have cooled frost and decorate with Mini Oreos.