We're going to dig deep into the dark days of the 1970s and uncover Buzz Capra, a small right-hander who the Braves purchased from the Mets in spring training of 1974. Capra began the season in the Atlanta but was later moved to the rotation and finished 16-8 with a 2.28 ERA, becoming one of the most anonymous ERA champions ever. Capra was a sidearmer who held hitters to a .208 average that year, including .158 against right-handers. Unfortunately, he suffered a shoulder injury in 1975 and would win just 10 more games in his career.
You could argue that the entire team was a two-time one-hit wonder, but if you want a player, how about Mark Redman? He was part of the 2003 World Series champion rotation, going 14-9 with a 3.59 ERA (although he didn't win any of his four playoff starts). Redman survived 10 seasons in the majors, but '03 was his only full season with an ERA under 4.00 (career ERA: 4.85). It's worth mentioning that he was an All-Star with the Royals in 2006 ... in a season he finished with a 5.71 ERA.
Mark Simon may have a different answer, but how about Bernard Gilkey? He had a couple solid seasons with the Cardinals, but in 1996 with the Mets he had an MVP-caliber season, hitting .317/.393/.562 with 30 home runs, 44 doubles, 117 RBI and 108 runs. Throw in some apparently nifty defense -- +23 runs via Baseball-Reference -- and he clocks in at 7.8 WAR, good for second in the National League. It ranks as the third-best season by a position player in Mets history behind David Wright's 2007 and Carlos Beltran's 2006. The next year he hit .249 with 18 home runs.
One of the all-time one-hit wonders is Jim Konstanty, probably the unlikeliest MVP ever. A 33-year-old bespectacled veteran reliever who had only spent one full season in the majors, Konstanty went 16-7 with a 2.66 ERA and 22 saves for the 1950 pennant-winning Whiz Kids. He threw a palm ball, a slider and a screwball, so didn't exactly blow hitters away (he struck out just 56 in 152 innings). His season impressed the MVP voters, however: He collected 18 of the 24 first-place, finishing ahead of Stan Musial, who hit .346 with 28 home runs and 109 RBIs.
Oddly, after not starting a game all season, Konstanty started Game 1 of the World Series against the Yankees. (In part because ace Robin Roberts had pitched 10 innings in the final game of the season to clinch the pennant.) Konstanty pitched well, but lost 1-0. Konstanty kicked around the majors for six more seasons and even saved 11 games for the Yankees in 1955, but never matched that magical 1950 season.
Did that Pedro Martinez guy ever do anything after leaving Montreal? John Patterson had been a first-round pick of the Expos in 1996, but was declared a free agent through a contract technicality. He signed with Arizona but eventually made his away back to the Montreal/Washington organization. In the club's first season in Washington, it all came together for him and he went 9-7 with a 3.13 ERA in 31 starts, striking out 185 batters in 198.1 innings. But he wasn't able to stay healthy and won just two more games in his big league career. If there's a moral of the one-hit wonders: Pitchers have short life spans.