Bake the cake in a round baking dish according to the directions on the box.

Once the cake has baked & has cooked, remove from the pan.

Using a sharp knife, carefully cut out a wedge from one side of the cake round. Take this wedge and cut it into two pieces: one piece will be shaped into the unicorn's ear, and the other piece into its horn.

Arrange these pieces creatively to bring the unicorn shape to life on a serving platter or cake board.

Frost completely with white frosting.

Cover the horn in yellow sprinkles.

Using the marshmallows, create the unicorn's mane.

Use the black frosting to draw on a mouth and eyes.