Spoon one of the tubs of marshmallow creme over the cake mix. With a spoon, gently swirl the two together. You don't want to mix; you should still see separate swirls of marshmallow and cake mix. Make sure you swirl the mixture to the end of the pan.
While cake is cooling, mix together frosting and the other tub of marshmallow creme. Frost cake with this mixture. Crush remaining graham cracker into fine crumbs and sprinkle over the top of the frosting.