1Heat oven to 350°F (325°F for dark or nonstick pan). Place paper baking cup in each of 26 regular-size muffin cups. Make cake batter as directed on box; fold in graham cracker crumbs and chopped chocolate bars. Divide batter evenly among muffin cups.
2Bake 18 to 23 minutes or until toothpick inserted in center comes out clean. Cool in pans 10 minutes; remove from pans to cooling rack. Cool completely, about 30 minutes.
3In large bowl, beat marshmallow creme, butter and powdered sugar on low speed until blended. Beat in enough milk, 1/2 teaspoon at a time, to make frosting spreadable. Spread over tops of cupcakes. Divide chocolate bar into rectangles. Cut each rectangle diagonally in half and place on top of each cupcake. Top each cupcake with bear-shaped cracker. After frosting has set, store loosely covered.