Preheat oven to 350°.
To prepare cake, lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 6 ingredients (through salt) in a large bowl. Add mayonnaise and oil; beat with a mixer at low speed until well blended. Slowly add brewed coffee and vanilla; beat with a mixer at low speed 1 minute or until well blended. Stir in chocolate; pour batter into a 13 x 9-inch baking pan coated with cooking spray. Bake at 350° for 30 minutes or until a wooden pick inserted in center comes out clean. Cool completely in pan on a wire rack.
To prepare mocha cream, combine water and coffee granules in a large bowl; stir until granules dissolve. Add marshmallow creme; beat with a mixer at low speed until smooth. Fold in whipped topping. Spread mocha cream over top of cake; drizzle with chocolate syrup. Chill until ready to serve.