Heat oven to 350ºF. Grease and flour 2 (2 1/2-quart) ovenproof deep bowls; set aside.
Combine all cake ingredients in another bowl. Beat at medium speed, scraping bowl often, until well mixed.
Divide batter evenly among prepared bowls. Bake 65-75 minutes or until toothpick inserted in center comes out clean. Cool 15 minutes; invert cakes onto serving plates. Cool completely.
Combine butter and 1/3 cup pumpkin in bowl. Beat at medium speed until well mixed. Gradually add half of powdered sugar; continue beating, scraping bowl often, until well mixed. Add remaining powdered sugar, milk and vanilla. Beat until smooth. Reserve 1/4 cup frosting. Stir in red food color to remaining frosting, if desired.
Cut narrow slice from bottom-side of 1 cake, using serrated knife. Place onto serving platter, cut-side down. Spread 1/2 cup tinted frosting over top of cake; place second cake over frosted layer, wide-side down.
Frost cake with tinted frosting. Cut licorice twists into 9 (1-inch) pieces; arrange on side of cake for eyes and nose. Cut 2 licorice twists to form mouth. Decorate with candies, if desired.
Add melted chocolate chips to reserved frosting. Place marshmallow on top of cake to form stem. Frost marshmallow with chocolate frosting.
*Substitute 2 tablespoons lemon juice or vinegar and enough milk to equal 2 cups. Let stand 5 minutes.
**Substitute canned pumpkin.