April can be a relatively slow time in terms of Minor League player promotions. Folks are getting settled into their opening assignments, trying to prove themselves before they can ascend to the next rung of the organizational ladder. At the same time, service-time rules can keep Major League-ready prospects on the farm a little longer than expected.
Regardless, there were more than a few movers among MLB.com's Top 100 overall prospects in the first month of the season. Below are Minor League promotions and Major League debuts that filled up transaction logs last month, along with a few big names who could be on the move next.

On the move within the Minors

Tigers RHP Casey Mize, Double-A Erie -- Many assumed the Tigers were going to keep last year's No. 1 overall pick in Class A Advanced Lakeland until the weather up north warmed up. But did anyone expect this level of dominance? Mize posted a 0.35 ERA and 0.31 WHIP while holding Florida State League batters to a .065 average and posting a 25/1 K/BB ratio in his four starts. He then tossed a nine-inning no-hitter in his first Eastern League outing. He ends April as the Minor League leader in average-against (.064) and WHIP (0.26), and there's a genuine wonder how long he'll stay with Erie. In short, this likely won't be the last time he features in a transaction log this season.

White Sox OF Luis Robert, Double-A Birmingham -- The White Sox returned Robert to Class A Advanced Winston-Salem to build him up after an injury-shortened 2018 with the Dash, and MLB.com's No. 37 overall prospect responded as one baseball's hottest hitters. He leads the Minors in average (.453), slugging (.920) and OPS (1.432) while hitting eight homers and stealing eight bases. He essentially forced the move to Double-A, where he should be challenged more regularly. If he stays healthy, Robert has all tools to continue his ascent in his age-21 season.

Phillies 3B Alec Bohm, Class A Advanced Clearwater -- The Phillies took a safe route by sending last year's No. 3 overall pick to Class A Lakewood to open his first full season, considering Bohm was drafted out of college. However, after some injury-related struggles in 2018, the decision had to do with trying to build some momentum to start the 22-year-old's pro career. Mission accomplished. Bohm hit .367/.441/.595 with three homers, three steals and a 14/12 K/BB ratio in his 22 games in the South Atlantic League, allowing the Phils to push him to Clearwater on the last day of the first month. He could be challenged in the offensively starved FSL, but Bohm is showing signs that he's much more of the hitter he was at Wichita State than he was during his struggles at Class A Short Season Williamsport last summer.
Rangers OF Julio Pablo Martinez, Class A Advanced Down East -- Unlike the others above, Martinez didn't exactly force the hand of his parent club before receiving his April promotion. But at 23, the Cuba native was on the older side of prospectdom for Class A when the Rangers moved him from Hickory to Down East on April 17 -- a transaction that coincided with Bubba Thompson's move to the injured list, meaning it was a crowded Wood Ducks outfield that had kept Martinez from Down East to begin with. The left-handed slugger has some work to do in his new home; he's gone just 6-for-45 (.133) with 19 strikeouts in his first 13 games in the Carolina League. But as he showed in a brief look in last year's Arizona Fall League, Martinez is capable of hitting tough pitching. That just has to carry over to 2019.
Other promotions of note: Luis Madero (Angels), Bryan Abreu (Astros), Huascar Ynoa and Jasseel De La Cruz (Braves), Ryley Gilliam (Mets), Gage Canning and Jackson Tetreault (Nationals), Kyle Dohy (Phillies), Ryan Rolison (Rockies), Gregory Soto (Tigers), Travis Blankenhorn (Twins), Zack Burdi and Steele Walker (White Sox)

Major League debuts

Blue Jays 3B Vladimir Guerrero Jr.: There's not mush to say that hasn't already been said here. The game's top overall prospect ascended to the Majors on April 26 after eight games with Triple-A Buffalo in which he went 11-for-30 (.367) with three homers and eight RBIs. Interestingly, Major League hurlers are already pitching Guerrero like a veteran, staying away from the plate and giving him a steady diet of outside breaking pitches. He hasn't quite shown the insanely good bat yet as a result, but if his past is any indication, Guerrero will make the adjustment and show everyone why he's still a favorite to win American League Rookie of the Year.

Nationals INF Carter Kieboom: Most believed Kieboom would work his way to the nation's capital at some point in 2019, and the Nationals prepared for that by getting him time at both shortstop and second base with Triple-A Fresno. But injuries to Trea Turner and Anthony Rendon necessitated infield help earlier than they'd have liked, and Kieboom did his part by flying out of the gate with a .379/.506/.636 line in the Pacific Coast League. He's made some hard contact in the Majors with two of his three hits leaving the yard, but he'll need to start making more consistent contact to force the Nats to keep him around and get him regular at-bats when Turner returns.

Angels RHP Griffin Canning: Much has been made about the move to Major League baseballs and the offensive explosion in Triple-A. That said, it only makes dominant pitching performances at the level stand out all the more. Canning fit that bill quite nicely early on, pitching to a 0.56 ERA and 0.94 WHIP while fanning 17 and walking only two in 16 innings with Salt Lake. Even better, the Angels allowed him to work deeper into outings; his six-inning performance on April 18 was the longest of his career after topping out at 5 2/3 innings last season. Some of that came from concerns about his shoulder coming out of UCLA in 2017. That seems to be in the past, and the Angels liked Canning's four-pitch mix enough to give him his debut Tuesday night against the Blue Jays. He sat around 93-94 with his fastball while mixing in a steady diet of sliders and curves while fanning six Toronto batters in 4 2/3 innings. As a result, it doesn't appear Canning is going anywhere any time soon.

Red Sox INF Michael Chavis: In a similar issue to Kieboom and the Nats, the Sox would've loved to see Chavis hit his way to the Majors at some point this summer. They probably wish it didn't take early IL stints for Dustin Pedroia, Eduardo Nunez and Bryce Holt to make it happen this quickly. But Chavis is certainly making it difficult for Boston to move him back to Triple-A Pawtucket. The 23-year-old right-handed hitter has hit two 441-foot homers -- the two longest struck by Sox hitters this season -- and has three total dingers along with a .313/.436/.625 line in 10 games. Despite his limited experience there, seven of his nine defensive starts have come at second base -- a sign Boston is willing to swallow his growing pains there in order to get his bat in the lineup. Expect more of the same, even when the others return healthy.

D-backs RHP Jon Duplantier: The D-backs called up their top pitching prospect on April 1 before the Minor League season even began and have used him to provide length in the Major League bullpen. After making appearances on April 1 and April 7, he was optioned to Triple-A Reno, where he made three starts but never threw more than 61 pitches in each of those outings. He returned to Arizona for one appearance on April 28, throwing four innings against the Cubs in a game that went 13 frames. He's back with Reno now but could get to know the route between Triple-A and the Majors quite well for now. Note: the 24-year-old right-hander has given up only one earned run in 16 2/3 innings between both stops while fanning 17 and walking 11. With three above-average pitches in his fastball, slider and curve, he's got the arsenal to handle a Major League starting assignment, but after previous injury woes, a future in the bullpen could be in view, too.
Other MLB debuts of note: Luis Rengifo (Angels), Alex Jackson (Braves), Lane Thomas and Ryan Helsley (Cardinals), Taylor Clarke (D-backs), Erik Swanson and Braden Bishop (Mariners), José Quijada (Marlins), Branden Kline (Orioles), Ty France (Padres), Cole Tucker, Bryan Reynolds and Jason Martin (Pirates), Taylor Hearn (Rangers), Nate Lowe (Rays), Darwinzon Hernandez and Travis Lakins (Red Sox), Josh Fuentes and Yonathan Daza (Rockies) Richard Lovelady and Kelvin Gutierrez (Royals), Mike Ford and Thairo Estrada (Yankees)

Who's next?

Reds OF Nick Senzel, Triple-A Louisville: MLB Pipeline's Jonathan Mayo reported Tuesday that the Reds' top prospect will head up to Cincinnati on Friday. Senzel missed the opening of the season with an ankle injury but returned to Louisville on April 23 and has hit .290/.333/.419 with one homer in his first seven games back with the Bats. All seven of his starts have come in center field, the position he was groomed for all spring. 

Astros OF Yordan Alvarez, Triple-A Round Rock: It isn't immediately clear where Alvarez would get playing time in Houston, but his bat has been as good as anyone's at Triple-A. His 11 homers are tied for the most at the level, and his .867 slugging percentage, 1.310 OPS and 201 wRC+ all rank second among Triple-A batters. He's started to get more playing time at first base, so it's possible Houston has its eye on letting him take over for Yuli Gurriel there. Making him the club's permanent designated hitter is also an option.

Brewers 2B Keston Hiura, Triple-A San Antonio: The Brewers made the unorthodox move to sign Mike Moustakas to play second base, but Hiura is hitting like a player that shouldn't stay down long. The 22-year-old has a .318/.351/.682 line with seven homers in 24 games with the Missions, showing more power than was to be expected from his already impressive bat. A couple more weeks of this, and Milwaukee will want to find a place for him to keep their place in a tight NL Central.

Cardinals 3B Nolan Gorman, Class A Peoria: The Cardinals pushed their 2018 first-rounder to the Midwest League last season and saw him show off his signature power with Peoria. It's been more of the same so far in 2019. Gorman hit .325/.389/.650 with six homers in 21 games with the Chiefs and ranks third among 240 Class A qualifiers with a 1.039 OPS. The 18-year-old doesn't have the college experience of Bohm that would allow to move out quite that quickly, but with 46 Class A games already under his belt dating back to last season, it's worth wondering when he'll see the Florida State League.

Dodgers RHP Dustin May, Double-A Tulsa: MLB.com's No. 65 overall prospect caught the Dodgers' eye with a strong spring before being sent back to Double-A Tulsa, where he posted a 3.67 ERA over six starts in 2018. He's been even better this time around with a 1.50 ERA, 0.96 WHIP, 27 strikeouts and seven walks over five starts (24 innings) back with the Drillers. Manager Dave Roberts seemed to expect to see May in Los Angeles at some point this summer, but first, he'll need to prove himself at Triple-A Oklahoma City. That look may not be far away.