Make and bake Chocolate High Cupcakes according to recipe directions. After the cupcakes have cooled, frost with vanilla buttercream frosting. Cover the cupcakes and set them aside.
To make the Batman cupcake toppers, roll out the black fondant on a clean and smooth surface. If the fondant is hard to roll, massage with your hands for a minute.
Using the circle stencil and a small, sharp knife to cut out 24 circles. Peel back the extra black fondant, roll it into a ball, and store in a zip-top plastic bag so it won't dry out.
Next, roll out the yellow fondant and cut out 24 ovals. Store the remaining white fondant in a zip-top plastic bag. Let the yellow fondant ovals dry completely.
Using the Batman-shaped stencil and the black edible ink marker, very lightly trace the Batman shape onto the yellow ovals. Be careful not to press too hard because your marker will sink into the fondant. Lightly color in the Batman shape and let the ink dry. You may need to go over it with a second coat if some of the yellow fondant is visible through the ink. Let the ink completely dry before assembling the toppers.
To assemble the cupcake toppers, dampen the center of one of the black circles with water, and place a yellow oval on top. The water will help hold the pieces together. Repeat this process to make each topper.
Let the fondant toppers completely dry, then place one on top of each frosted cupcake.