Bake and cool cake according to pan directions. Place on a foil-wrapped cake board cut to pan shape.
Prepare buttercream icing. Tint portions gray, green and black; leave some white. Ice pumpkin and inside of eyes, mouth and nose cavities with spatula and gray icing.
Pipe black decorating gel in eyes, nose and mouth cavities; brush smooth. Insert gum into mouth.
For eyes, pipe ball, 1 1/4 in. dia., with tip 2A and white icing. Pipe irises with tip 2 and green icing; pat smooth with finger dipped in cornstarch. Pipe pupils with tip 2 and black icing; pat smooth.
For eyelashes, cut black shoestring licorice 3/4
in. to 1 in. long. Attach around eye cavities with gray icing. Use red decorating gel for veins and blood.
For worms? tongues, cut red shoestring licorice into 1/4
in. pieces; cut small ?V? on one end. Cut a small slit into head of worm; insert tongue. Position worms on top of cake. Pipe dot eyes on worms with tip 1 and black icing.