Prepare royal icing and tint portions green, orange and black. Use tip 2 and full-strength green royal icing to outline stems, and tip 2 and full-strength orange royal icing to outline pumpkins. Use tip 2 and thinned green royal icing to fill in stems, and tip 2 and thinned orange royal icing to fill in pumpkins. Let dry on waxed paper overnight.
When dry, use tip 3 and full-strength black royal icing to pipe facial features. Let dry. Attach cookie sticks to back of cookies with tip 2 and full-strength orange royal icing.