3) Harrison Bader
Harrison Bader was the player the Yankees acquired when they sent Jordan Montgomery to the Cardinals, so it'd be ironic if the Mets brought them both to Queens. Bader was a long-time Cardinal before his year in the Bronx. He's had his ups and downs throughout his career, and his time with the Yankees was no exception.
He was limited to just 14 regular season games with the Yankees last season as he was recovering from injury, but in the postseason he became somewhat of a folk hero, carrying them to an ALCS appearance. This past season Bader missed time due to injury (as he often does) and took a bit of a step back offensively.
With the Yankees out of contention they placed Bader on waivers where he'd eventually get picked up by the Reds. His offensive numbers weren't great, as he slashed .232/.274/.348 with seven home runs and 40 RBI, but this is still an intriguing player the Mets should consider.
As things stand right now, the Mets don't have a fourth outfielder. Yes, D.J. Stewart is capable in the corners, but he's not the traditional fourth outfielder who can play all three outfield spots. Bader on the other hand, is one of the better defensive center fielders in the game. That's where his game shines.
The Mets are known to sign the speedy defensive-minded fourth outfielder as they seem to do it every year, but Bader would provide a bit more with the bat than those guys. He's not the best hitter in the world, but he's not an automatic out either. Bringing the 29-year-old New York native to Queens to be the team's fourth outfielder who'd also be a capable fill-in if a starter went down makes a lot of sense.