There's a chance that the New York Mets would have made the playoffs and gone on a run into the World Series if they hadn't acquired Yoenis Cespedes at the trade deadline last year, but the only thing we know with certainty is that they did acquire Cespedes and did make it to the World Series.
When the Mets traded pitching prospects Michael Fulmer and Luis Cessa to the Detroit Tigers for Cespedes just minutes before the trade deadline, they had wrapped up an incredibly awkward week. Wilmer Flores and Zack Wheeler had nearly been traded for Carlos Gomez, but that deal fell through. The Mets lost a brutal game to the Padres in between rain delays. Other moves had been made, and Michael Conforto had just been promoted to the big leagues, but the Cespedes trade felt a whole lot more significant than anything else that Friday afternoon.
All Cespedes did for several weeks following the trade was hit like Mike Trout. In total, he made 249 plate appearances for the Mets in the regular season and hit an absurd .287/.337/.604 with 17 home runs. He took to center field reasonably well, considering his primary position in his major league career had been left field, and made some outstanding throws from the outfield—not that those came as any surprise.
Things didn't go as well in the playoffs, though Cespedes hit two home runs in the NLDS—one of them one of the best no-doubt home runs in Mets history as the team trounced the Dodgers in Game 3. In total, he hit .222/.232/.352 in 56 postseason plate appearances, and he had a couple of poorly-timed miscues in center field during the World Series. On the upside, he debuted a customized walk-up song in the process.
That he proved to be human disappointed some Mets fans, of course, but Cespedes hit 37 home runs in 173 total games in 2015 and seemed destined to leave in free agency.
Fortunately, the Mets and Cespedes shocked everyone when they agreed to a three-year, $75 million contract in January. The deal includes an opt-out clause after the first season, and it wouldn't be surprising at all if Cespedes takes advantage of that option. For now, though, he's back for the upcoming season and helps make the Mets one of baseball's World Series favorites. That'll do.