Place templates on sheet cakes, and cut out with a paring knife. Halve eye, beak, and brow pieces horizontally. Reserve scraps.

Arrange pieces into an owl shape, using scraps to build up chest.

Starting with 9 1/2 cups buttercream, reserve 2 1/2 cups and tint the rest yellow. Use yellow buttercream to attach pieces. Coat eyes with untinted buttercream and rest of cake with yellow, rounding over chest. Refrigerate until frosting is firm, about 30 minutes and up to overnight. Add a second smooth coat of untinted buttercream to top surface of eyes. Add a second smooth coat of yellow to beak and edges of eyes. Layer yellow frosting on wings and head, creating grooves with a small offset spatula. Fill a pastry bag fitted with a medium petal tip (Ateco #103) with 1 cup untinted frosting and 1 cup yellow, the two side by side. Holding bag at a 45-degree angle, with the thinnest opening of the tip facing up, pipe ruffles in vertical lines to cover chest. Pipe 2 lines of ruffles on each brow.

Place a chocolate wafer cookie on each eye, and top each with a Necco wafer, using a dab of frosting to adhere. Halve 6 cookies, and use as talons. Halve another cookie, break off the top of each half, and use as beak.