You can make a case for a dozen or more Mets having plenty to prove going into the 2020 season, from the high of Pete Alonso looking to validate his historic rookie season to the low of Edwin Diaz needing to bounce back from his abysmal first year in New York.
With input from scouts I spoke to on Wednesday, here are the five I consider most interesting -- in part because of their uncertainty -- and potentially most impactful.
1) Yoenis Cespedes
The intrigue level in spring training alone will be sky-high as Cespedes tries to prove he's not just a punch line for wild boar jokes at this point, attempting at age 34 to come back from double-heel surgery and a broken ankle, while having played in only 38 games the last two seasons.
Motivation has always been the knock on him, but if Cespedes is ever going to be driven to produce on a daily basis it's 2020, knowing he can earn back some of the millions he lost in the boar-related contract reduction, as well as convince some team to sign him next winter after his deal with the Mets expires.
Two scouts I spoke to made the case that he'll still be a productive hitter, noting that someone with his explosive athletic ability should age well into his late 30s -- if he can avoid more significant injuries.
"Go back and look at those workout videos he posted when he came over from Cuba (in 2011)," one scout said. "I'll never forget seeing him doing those high box jumps like it was nothing, as well as some of the other stuff. Obviously he's older and heavier now but you don't lose that fast-twitch athleticism just because you've been hurt."
I did take a look at that old video on YouTube and it is indeed remarkable to see a, yes, noticeably slimmer Cespedes doing 45-inch box jumps, not to mention 1,300-pound leg presses that may or may not have eventually contributed to his various quad and hamstring strains.
In any case, even if all of his injuries surely have dulled some of the explosiveness in his legs, his athleticism does offer reason to believe Cespedes could still be a force with the bat and able to play an adequate left field.
But is it realistic to think those legs won't give him problems of some type across 162 games? Probably not, which is why the Mets should be smart enough to keep him rested and playing only semi-regularly even if he's healthy as a precaution against further injury.
Even in that case, starting maybe four times a week and looming as a late-inning bat off the bench on other days, a resurgent Cespedes could be the type of wild card the Mets would need to have a real shot at winning the NL East.
2) Robinson Cano
As late as July 31 last season, Cano was hitting .235 with a .663 OPS, looking for all the world like he'd gotten old the minute he'd put on a Mets jersey, in the not-so-grand tradition of Roberto Alomar and Carlos Baerga.
But then, out of nowhere he had a 9-for-16 stretch that included four doubles and a home run, only to tear a hamstring and miss a month, yet still came back to have a solid September, hitting .277 with an .856 OPS, offering hope that he's not washed up just yet.
So was it the injuries to his hands -- the result of a few hit-by-pitches, as Cano himself indicated -- that made him look so bad at the plate for so long? Even scouts admit they're not sure.
"I'll be honest, I thought he'd lost some bat speed, judging by the way he seemed to be cheating to get to the fastball," one scout told me Wednesday. "I'd never seen him do that before.
"One of the reasons he was always such a good off-speed hitter was because he trusted his hands on the fastball, and he was so good at taking a pitch the other way with a flick of his wrists. But then last year it looked like he was starting his swing early because he was worried about getting beat, and he wasn't as good on the off-speed stuff.
"But then late in the year he looked a lot more like himself again, still quick enough to pull a fastball without committing himself too early. So maybe he was protecting an injury. He's such a natural hitter that I'd bet on him still having something left."
You'd think Cano will be determined to prove that, and perhaps even motivated to reward his old agent, Brodie Van Wagenen, for taking a chance on him and getting him out of Seattle.
3) Noah Syndergaard
There still seems to be an expectation around the game that Syndergaard will rediscover his one-time dominance and pitch at an elite level again with more consistency. But after the worst overall season of his career, it's surely time for the 6-foot-6 right-hander to prove such expectations are realistic as he enters his age-27 season.
At times last year, it seemed Syndergaard was a mess mentally, perhaps affected by the 2019 baseball with lower seams that had him lamenting his inability to throw his once-unhittable slider.
In any case, his 4.28 ERA (3.60 FIP) was telling enough. But even more revealing, his ERA+ number (taking into account ballpark effects) was 95, below league-average and by far the worst of his career.
"His stuff is too good for him to have a year like that," one scout said. "But he's getting to the point where you have to ask if he'll figure it out. If he does, as the No. 2 behind (Jacob) deGrom, the Mets have a great rotation. If he doesn't, they're probably only about average."
4) Edwin Diaz
Diaz's bizarre 2019 season might be best summed up by his disparate statistical extremes: he gave up 15 ninth-inning home runs, the most in major league history, while pitching to a 5.59 ERA (4.51 FIP), yet still racked up 15.4 strikeouts per nine innings, a rate slightly higher than he had during his spectacular 2018 season for the Mariners.
And considering he's the single most significant reason the Mets didn't make the postseason, nobody has more to prove than Diaz.
Was it mechanics? Was the stage too big for him?
"Everybody talks about the slider command but sometimes he was missing location with his fastball by a couple of feet," said one scout. "So I don't know what to make of him. If he finds any sort of command, he could be lights-out again and then that Mets bullpen could be really, really good."
5) Marcus Stroman
A strong September changed the narrative a bit on Stroman after he initially failed to deliver on his own big talk upon coming over from the Blue Jays, saying he was made for the big stage in New York.
He pitched to a 2.91 ERA in the final month -- two runs lower than he did during his first five starts as a Met -- and if he can pitch at that level in 2020, the Mets' rotation could live up to Van Wagenen's pronouncement as the deepest in baseball.
In search of a big free agent contract after next season, Stroman will have to prove he can be as dominant as he often says he is.
"I like his cockiness, it's part of what got him here at 5-foot-7," said one scout. "But I don't think he's more than a solid No. 3 starter, because he has to get guys to chase his slider and two-seamer below the zone to be effective, and it's hard to be consistently dominant pitching that way."