St. Louis Cardinals, as Mancuso had an off-year with his batting average dropping almost twenty points along with 10 fewer runs batted in. In 1935 Mancuso improved to hit for a .298 batting average with five home runs, and 56 runs batted in. He also earned a spot as a reserve for the National League team in the 1935 All-Star Game. He had his best season in 1936, hitting for a .301 batting average with career-highs of nine home runs and 63 runs batted in as the Giants once again claimed the National League pennant. He led the league's catchers in putouts, baserunners caught stealing, finished second in assists and, once again guided the Giants' pitching staff to the lowest earned run average in the league. The Giants would go down in defeat against the powerful New York Yankees in the 1936 World Series. Mancuso finished the year ranked eighth in voting for the 1936 National League Most Valuable Player Award. In 1937, Mancuso was hitting for a .283 average at mid-season to earn his second berth as a reserve for the National League team in the 1937 All-Star Game. A few days after the All-Star Game, a foul tip broke the ring finger on Mancuso's right hand. Harry Danning replaced him and played well enough that, when Mancuso was healthy again, the two shared the catching duties for the rest of the season. The Giants clinched their second consecutive National League pennant and, once again faced the New York Yankees in the 1937 World Series. Mancuso started the first two World Series games but, when he went hitless, Danning took over as the Yankees went on to win the series in five games. Danning took over as the Giants' starting catcher for the 1938 season with Mancuso hitting a respectable .348 with a .411 on-base percentage in 52 games. The Giants traded Mancuso to the Chicago Cubs before the 1939 season where he shared catching duties with 38-year-old player-manager Gabby Hartnett. He ended the season with a .231 batting average with only two home runs and 17 runs batted in. With the shortage of major league players due to the Second World War, Mancuso saw his career extended for another four years. He played the 1940 season with the Brooklyn Dodgers before the Cardinals brought him back to St. Louis for the 1941 season. Mancuso helped develop the Cardinals'