Some players are on the verge of stardom, others are entering a crucial phase of their development and still others are getting their first tastes of full-season ball. With the 2016 season approaching, MiLB.com takes a look at the most intriguing prospects from each MLB organization.
Back and healthy: Marco Gonzales, LHP
Gonzales sped through the Minors to start his career, making his Major League debut in his first full season. But in his third campaign, he ran into some speed bumps along the way.
Beginning 2015 with Triple-A Memphis, Gonzales seemed primed to return to the Majors in no time. He missed three starts when he felt tightness in his left pectoral muscle in April, then three outings later, he returned to the disabled list with a similar shoulder issue.
After returning on July 10, Gonzales showed his resilience as well as an above-average changeup as he rehabbed and climbed through the system once again. The hard work paid off as the Cardinals' No. 7 prospect returned to Busch Stadium on Sept 1 for a start against the Nationals.
"He's ready to go this year, and we're looking forward to a real productive year from him. When you think back, he's only a few years removed from the Draft process and he came through the system quick as well," said Gary LaRocque, the Cardinals' director of player development. "This will be a good year to see him through the entire year and stay healthy through the year and have him help us [in St. Louis]. He has his sights clearly set on that and we look forward to him being part of it."
Breakout prospect: Carson Kelly, C
According to LaRocque, Kelly has already begun to break out. And behind the plate that certainly appears to be true. The converted catcher threw out 3 percent more would-be base stealers and cut his errors down to three with Class A Advanced Palm Beach last season. Kelly's efforts won him a Gold Glove as top backstop in the Minors.
But now the Cardinals' No. 13 prospect will be looking to break out at the plate. Kelly flirted with the Mendoza line for the first half of the season, but once July rolled around, he took off. In the final two months of the season (plus three games in September), the 21-year-old hit .268 with five of his eight home runs.
"We were pleased with the progress, his development. Looking forward to this year, just getting back at it. He's come up to the level of the Florida State League as a hitter and now we're looking forward to the next challenge," LaRocque said. "I think he's right on track and has just a great, great desire. We're looking forward to a real strong year."
Major League-ready: Sam Tuivailala, RHP
Tuivailala spent the season bouncing between the Majors and the Minors last season, but it didn't affect his stats, as the reliever posted a 1.60 ERA with 43 strikeouts and 17 saves in 43 appearances with Memphis.
"The thing he is learning to do now is to develop the ability to get his secondary stuff over. He clearly has arm strength and he's learning how important the fastball command is. It's still a learning process," LaRocque said. "He's doing very well with it. He's obviously worked his way through the system well and we're looking forward to a good year out of him."
Tuivailala has an 80-grade four-seam fastball that can reach the upper 90s, and the Cardinals asked their No. 11 prospect to add a cutter. With his strong arsenal, the 23-year-old did not allow a run over his first four spring outings at big league camp, striking out seven in four innings.
Full-season debutant: Casey Grayson, 1B
Grayson tore up the New York-Penn League last season, tying for the circuit lead with 77 hits and 46 walks. The 24-year-old also ranked in the top five of the league in average (.308), OBP (.414), RBIs (38), total bases (105) and OPS (.834).
The first baseman stayed sharp with the glove too, committing just four errors in 73 games while also playing one game in right field. While Grayson isn't ranked, the left-handed hitter is set to turn heads with a full-season spotlight in 2016.
"He put together a real strong year in the short season, and we really feel as though that'll translate into a full season," LaRocque said. "He's already off to a solid start in this Spring Training, so we're looking forward to 2016 being a positive year for Casey."
Shining star: Alex Reyes, RHP
For the second year in a row, Reyes will not be able to be on the mound all season long. But if 2015 is any indication, he'll still blow hitters -- and stats -- away when he is on the rubber.
The Cardinals' top prospect battled injuries last season, but still ended up leading the system with 151 strikeouts. This year, Reyes will begin the campaign by finishing off a 50-game suspension for marijuana use, which he began to serve during the Arizona Fall League.
"It was a huge mistake I'm learning about. I'm learning how to get past it. It's been tough dealing with the problems and everything," Reyes said at the Cardinals Caravan in January. "I'm looking forward to next season and just putting this behind me and turning the chapter on this."
With an above-average fastball, Reyes was the Cardinals' Co-Minor League Pitcher of the Year in 2015 after notching a career-best 2.94 ERA in 22 starts across three levels before playing in the AFL. MLB.com's No. 13 overall prospect pitched in Minor League camp and will continue to work in extended spring training until the suspension is completed.
"We're really looking forward to building him up and getting him ready over the course of the next four or five weeks," LaRocque said. "He's learning more about himself in terms of his fastball command, developing that, the continuation of developing his breaking ball and learning how to pitch soft when he needs to. But at the same time, he has very good stuff."
More to keep an eye on: First baseman Luke Voit sparked Palm Beach, leading the squad in just about every offensive category. This season, he should get the chance to show off his talents in the Texas League, a more hitter-friendly circuit. Voit shared the organizational lead of 77 RBIs with Jacob Wilson, who also topped the system with 18 homers. The third baseman finished the season in Triple-A, and if he continues to progress, expect to see him in St. Louis this summer. Southpaw Austin Gomber shared the club's top pitcher honors with Reyes after an organization-best 15 wins. He'll look to build on that success this season in the pitcher-friendly Florida State League.
Kelsie Heneghan is a contributor to MiLB.com. Follow her on Twitter @Kelsie_Heneghan.