Take grey buttercream with tip 5 and pipe the helmet visor. Pipe a long rectangle that is rounded as pictured. Hold the piping bag at a slight angle towards you so the buttercream flows out like a tube of toothpaste. Pipe back and forth until its filled.
Pipe a small strip of blue buttercream as a detail at the top of the helmet, use tip 5, outline and fill it in.
Use white and tip 5, Pipe a round circle bordering the cookie but leaving the neck unfrosted.
Fill in the circle but careful not to pipe over the grey and blue already piped.
Attach tip 12 to the white, hold piping bag straight up and down, about ¼ inch off the cookie, at the base of the circle where the neck is. Squeeze a large amount of pressure and pipe along the bottom for the neck and then stop where the cookie ends.
Take a mini marshmallow and cut it in half short ways to have two small stubby ends of the marshmallow. Place each piece on either side of the helmet.
Take tip 2 and red buttercream. Pipe an apple on the bottom of the helmet where the neck is. Outline and fill it in.
Take yellow or white buttercream and tip 1 and pipe tiny dots on the apple.
Use tip 2 and brown buttercream, pipe a stem for the apple, then use green and tip 2 and pipe a small leaf to complete the cookie.