Prepare pudding mix according to package directions, except stir in several drops of green food coloring with the milk until desired color is reached. Chill as directed.
Meanwhile, place crushed sandwich cookies in a shallow dish. If necessary, remove paper bake cups from chocolate cupcakes. Using a spoon or sharp knife, hollow out centers of cupcakes to form cauldron shapes, leaving 1/2 inch around the edges and about 1 inch on the bottom of each. Spread Chocolate Butter Frosting on the sides of cupcakes. Holding a cupcake by the top over the dish, sprinkle cookie crumbs around the base to coat. Repeat with the remaining cupcakes. Spread the remaining chocolate frosting around the top rims of cupcakes. Sprinkle with remaining cookie crumbs; shake off excess.
Spoon a generous tablespoon of the green vanilla pudding into the center of each cupcake. Decorate pudding with decorating gel and sprinkle with small green candies. Cut twenty-four 3-inch lengths of licorice. Using two licorice pieces for each cupcake, push the ends of licorice pieces into opposite sides of each cupcake rim to make a handle. Press one Cauldron Stirrer at an angle into each cupcake. Makes 12 (2-1/2 inch) cupcakes.
Chocolate Butter Frosting
In a very large mixing bowl beat butter with an electric mixer on medium speed until smooth. Beat in cocoa powder. Gradually add 2 cups powdered sugar, beating well. Slowly beat in 1/2 cup milk and vanilla. Gradually beat in an additional 6 cups powdered sugar. Beat in additional milk, 1 tablespoon at a time, as needed to reach spreading consistency. Makes enough to frost tops and sides of two 8- or 9-inch layers.
Set a wire rack over waxed paper. In a small microwave-safe bowl combine chocolate pieces and shortening. Microwave on 100 percent power (high) for 1 to 2 minutes or until melted, stirring every 10 seconds. Place a pretzel stick on the tines of a fork. Spoon melted chocolate over pretzel to coat completely. Place pretzel on rack. Repeat with the remaining pretzel sticks and the remaining melted chocolate. Let stand until chocolate is set.