1Heat oven to 350°F. Line 12-inch pizza pan with foil; grease foil with shortening. Make brownie mix as directed on box, using water, oil and eggs. Spread batter in pan.
2Bake 26 to 30 minutes or until toothpick comes out almost clean. DO NOT OVERBAKE. Cool completely on cooling rack, about 1 hour.
3Frost brownie with vanilla frosting. Place chocolate chips in small resealable food-storage plastic bag. Place in bowl of very hot water; let stand until chips are melted. Cut off tiny corner of bag. To make spiderweb, pipe melted chocolate on frosting in spiral pattern, starting at center and keeping lines about 3/4 inch apart. Using toothpick or knife, draw lines outward through frosting, starting at center of brownie.
4Cut gumdrop crosswise into thirds. Place small rounded end, rounded side up, on brownie for spider body. Cut 4 thin strips from each remaining gumdrop slice for legs; place on each side of spider body.