Line a 13x9-inch baking dish with waxed paper; set aside. Place crispy rice cereal in large bowl; place crushed cocoa crunchies in second large bowl; set aside.
In large saucepan, melt butter over low heat. Add marshmallows and stir until melted and smooth. Cook 2 minutes longer, stirring constantly. Remove from heat.
Pour half marshmallow mixture over crispy rice cereal; stir until well coated. Press mixture firmly into baking dish. Pour remaining marshmallow mixture over crushed cocoa cereal; stir until well coated. Press mixture firmly onto the top of the crispy rice layer. Allow to cool for 2 minutes.
Remove waxed paper from pan. Roll the marshmallow mixture lengthwise until it forms a log. Roll log in wax paper and place in refrigerator for 15 minutes. Unroll and cut into 12 slices.