Reynolds spent the 2015 regular season in Triple-A before being called up to the Mets during the 2015 NLDS to replace the injured Rubén Tejada. In doing so, he became the first player in modern baseball history to be added to a postseason roster in the middle of a series without previous major-league experience. He also became the third player in modern baseball history to be included on a postseason roster without previous major-league experience, after Chet Trail (of the New York Yankees in the 1964 World Series (not on the active roster)) and Mark Kiger (of the Oakland Athletics in the 2006 American League Championship Series). He was dropped from the roster for the World Series, and did not appear in any games in the playoffs.