Decorate cake. Use tip 10, a cut disposable decorating bag and white decorator icing to outline and pipe in oval eyes. Pat smooth with finger dipped in cornstarch. Tint reserved chocolate icing black. Use tip 10, a cut disposable decorating bag with coupler and black icing to pipe dot pupils and oval nose. Pat smooth. Use tip 2 and black icing to pipe dot whiskers. Insert antlers just before serving.