Prepare a red velvet cake mix and preheat oven according to package directions. Grease a 9-by-5-inch loaf pan. Slice a store-bought pound cake into 1/2-inch-thick slices. Cut a shape from each slice with a festive cookie cutter. Firmly pack cutouts upright in loaf pan. Pour 4 cups cake batter on top. Bake according to directions, about 40 minutes. Set on a rack to cool, then remove cake from pan and let cool completely. Top with confectioners' sugar.