Preheat oven to 350°. Prepare cake mixes according to package directions. Pour batter into 2 greased 1.5-qt. ovenproof bowls and 2 greased 10-oz. custard cups.
Bake until a toothpick inserted in the center of each cake comes out clean; 40-45 minutes for custard cups and 60-65 minutes for bowls. Cool in pans for 5 minutes before removing to wire racks to cool completely.
For frosting, beat shortening and butter in a bowl. Beat in confectioners' sugar, vanilla and enough milk to reach spreading consistency.
Use a serrated knife to level the cakes. Place 1 large cake flat side up on an 8-in. serving plate. Frost top of cake. Place remaining large cake on top with the flat side down and edges even. Frost top and sides.
For the head, place 1 custard-cup cake with flat side up on serving plate. Frost top of the cake. Place remaining custard-cup cake on top with the flat side down and edges even. Frost top and sides. Trim 1 side of assembled head so it is flat, then place head above the body, using extra frosting to adhere.
To decorate the cake, use orange Reese's Pieces to create four 3-inch circles randomly placed on the body. Arrange silver nonpareils and additional orange Reese's Pieces in decorative patterns inside each circle. Use additional orange Reese's Pieces and nonpareils to form parallel lines at the top and bottom of the head. Place 1 mini Oreo and 1 brown Reese's Pieces candy outlined with nonpareils in between the parallel lines to make the cameras. Insert pretzels sticks into head for antenna, leaving 1 longer than the other.