Make cupcakes: Preheat oven to 350°F. Line a 12-cup muffin tin (or mini-cupcake tin) with cupcake liners. In a medium bowl, whisk together flour, baking powder and salt; set aside. Using an electric mixer, cream butter and sugar together until light and fluffy. Add eggs and vanilla and beat well. Add dry ingredients alternately with milk, scraping down sides of bowl after each addition.
Fill each muffin cup about twothirds full. Bake until tops are springy to touch, 20 to 25 minutes (about 10 minutes for mini cupcakes). Cool in tin on wire rack. (Cupcakes can be made to this point and kept, in an airtight container, for 1 day.)
Make frosting: Using an electric mixer, beat together butter and shortening for about 2 minutes. Slowly beat in confectioners' sugar a little bit at a time. Beat in vanilla and salt, and continue beating for another minute until wellcombined. (Frosting can be made up to 1 week ahead; refrigerate in an airtight container and beat again before using.)
Divide frosting among separate containers for each color you wish to use, and add food coloring; leave some uncolored if desired. Frost cupcakes with an icing spatula.
Use assorted icing tubes to make hair, and use assorted candies to make faces.