1Heat oven to 350°F (325°F for dark or nonstick pan). Grease or spray bottom only of 13x9-inch pan. In large bowl, beat cake mix, cracker crumbs, water, sour cream, oil and eggs with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Pour into pan.
2Reserve 1/4 cup hot fudge topping. Drop remaining hot fudge topping by generous tablespoonfuls randomly in 12 to 14 mounds onto batter in pan.
3Bake 40 to 46 minutes or until toothpick inserted in center comes out clean. Run knife around side of pan to loosen cake. Cool completely, about 1 hour.
4In medium bowl, stir together marshmallow creme and frosting. Frost cake with marshmallow frosting. Drop small dollops of reserved hot fudge topping randomly over frosting. Swirl topping through frosting with knife for marbled design. Store loosely covered.