Line a 13x9x2-inch baking pan with foil, allowing foil to extend over edges of pan; set aside. Prepare brownie mix according to package directions using the prepared baking pan. Cool brownie in pan completely. Use foil to lift brownie from pan onto a cutting board. Remove foil. Using the bottom of a 9-inch springform pan as a guide, cut a circle from brownie. Place the brownie circle in a 9-inch springform pan (eat remaining brownie scraps or save for another use).
Spoon softened ice cream over brownie in pan, spreading evenly. Cover and freeze for 2 hours. Sprinkle with cookie crumbs over top of ice cream.
For ears, press in blue tortilla chips. For cat eyes, press a small cutout piece of fruit leather onto each white gum ball; press into cake. Add an orange gum ball for the nose. For whiskers, add green twists, trimming as necessary. For mouth, color about 1/3 cup fondant yellow and another 1/3 cup fondant orange. Alternate 2x1/2-inch pieces of the colored fondant on a piece of waxed paper, placing the pieces close together. Roll out fondant to about 1/4-inch thickness. Cut out a "smile" shape; place on cake. Cover and freeze cake until firm, at least 4 hours or up to 24 hours.
To serve, remove sides and bottom of pan and place on a platter. Makes one cake (12 servings).