Aroldis Chapman
On July 25, 2016, the Cubs made the move to solidify the roster during the World Series run. Aroldis Chapman came over from the Yankees, in exchange for top prospects Gleyber Torres and Billy McKinney, along with Rashad Crawford, and major league piece arm Adam Warren.
In a way, the Cubs were able to turn Starlin Castro into Ben Zobrist and Aroldis Chapman. Not bad, huh?
Chapman was dominant, like he normally is, during his time with the Cubs…albeit for one appearance. In game 7 of the World Series, which the Cubs won, Chapman came in to hold a 3-run lead in the eighth inning, and could not hold the lead. Part of that was him being overworked throughout the playoffs.
The acquistion of Chapman was not very well-received amongst Cubs fans, mostly because of his past with the domestic assault allegations. However, without Chapman, the Cubs almost certainly do not win the World Series.