Decorate Minions cakes also 1 day in advance. Prepare royal icing. Tint small portions black, gray and brown; reserve a small portion white. Tint remaining royal icing yellow and blue.
Use spatula and yellow royal icing to ice back of mini cake and top 3/4 of front smooth. Place on parchment-covered cake board. Position licorice hair. Let icing crust slightly, about 20 to 30 minutes.
Use 12 in. decorating bags to decorate mini cakes. Use tip 8 and blue icing to fill in overalls; pipe outline straps. Use tip 8, decorating bag and yellow icing to pipe outline arms. Use tip 12 and blue icing to pipe pull-out legs. Use tip 8, decorating bag with coupler and black icing to pipe dot gloves and shoes. Use tip 8 and white icing to pipe in eyes. Use tip 4 and brown icing to pipe dot pupils. Use tip 4 and gray icing to pipe outline lenses. Use tip 4 and black or gray icing to pipe zigzag glasses frames. Use tip 2 and black icing to pipe outline smile, dot irises and details on overalls.
Insert lollipop stick in bottom of four mini cakes, leaving 5 in. extended at bottom to be inserted in cake top. Let cakes dry on parchment-covered cake board overnight.