Make candy antlers 1 day in advance. Copy pattern and tape to cake board. Cover with parchment paper. Melt a portion of dark cocoa Candy Melts candy in disposable decorating bag according to package directions. Cut a small point off of disposable decorating bag. Use melted dark cocoa candy to outline and fill in antler pattern. Reverse pattern and repeat for opposite antler. Chill until firm, about 10 to 15 minutes. Carefully remove and turn over candy antlers on parchment paper.
Attach pretzel rods to antlers. Melt remaining dark cocoa Candy Melts candy in tall dipping container according to package directions. Dip two pretzel rods halfway in candy. Immediately place dipped pretzel rods on antlers. Chill until firm, about 10 to 15 minutes.
Make layered cake. Prepare batter following recipe directions. Bake and cool two 6 in. cake layers. Level, fill and stack layers on same-size cake circle for a 2-layer cake, 4 in. high. Use spatula and chocolate decorator icing to ice cake smooth. Reserve remaining chocolate icing.
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.