In advance: Using pan as a pattern, prepare same-size cake board; wrap with foil.
Prepare cereal treats mixture and press into lightly greased pan. Release immediately onto waxed paper-covered board. Position on prepared cake board; use knife to trim cereal as needed.
Ice saddle and rocker base smooth. Pipe tip 12 outline on saddle (pat smooth with finger dipped in cornstarch). Using tip 6, pipe number; pipe outline bridle (pat smooth). Use icing dots to attach mini candies to saddle and bridle; attach regular-size candies for eye and on rocker. Outline and pipe in hooves with tip 6 (smooth). Pipe tip 18 pull-out star mane and tail.