Several days in advance, make color flow leprechaun on waxed paper using pattern. Outline and flow in using tip 2; let dry. Using full-strength color flow, pipe tip 1 facial features, tip 2 buckles, buttons, dots, hair and beard. Make extra to allow for breakage. Set aside.
Ice sides of shamrock cake smooth. Cover top of cake with tip 20 stars; add tip 20 star bottom border. Position sugar cubes where leprechaun will rest. Trim waxed paper around leprechaun; leave remainder attached to back. Position leprechaun, icing decorations and curling ribbon.
The star tip creates the most celebrated, easily accomplished decorations! The serrated edges of the star tip make ridges in the icing as you squeeze it out. Because fill in requires so much piping from the same bag, keep replenishing icing in bag.