3 Diamondbacks Prospects Whose Stock Is Soaring in 2025

With more than six weeks of games in the books, prospects are starting to separate based on their performances in the 2025 season. As we prepare for our midseason prospect rankings update here on Arizona Diamondbacks on SI, these three prospects in Arizona's system have made the case for a promotion to the next level.

The three prospects highlighted include a young starter potentially breaking out at the top level of the minor league system, a former top outfield prospect who has bounced back after three lost seasons, and a flamethrowing reliever who may one day serve as the primary setup man to future closer Justin Martinez.

RHP Cristian Mena (No. 12)

In eight outings between Triple-A and the major leagues, Mena is 2-3 with a 4.42 ERA. The right-hander has shown improved control and command, with 45 strikeouts and 14 walks over 38.2 innings. Opposing hitters are batting just .236 against him this season.

While Mena's 4.89 ERA on the season is higher than the 4.61 mark he posted in 2024 with Triple-A Reno, the peripherals are much better. He's improved his strikeout rate from 24.1% to 27.0% while simultaneously cutting his walk rate from 10.8% to 8.3%. At the same time, his home run per nine has dropped from 1.41 to 1.29.

No outing perhaps, has done more to improve his stock than a relief appearance against the Los Angeles Dodgers on May 9. Facing the best offense in baseball, Mena fired 3.2 hitless innings with one walk and five strikeouts. It gave the Diamondbacks a chance to make a comeback, as he entered an 8-3 game and exited with a 9-8 lead. He was three outs away from his first career win.

Mena hits mid-90s with both a four-seamer and sinker, but his standout pitch is his curveball. In Triple-A, it's averaging 87.0 MPH with -2.1 inches induced vertical break and 1.9 inches of glove-side break. Due to the velocity and break of the pitch, it essentially functions a lot like a gyro/death ball slider. The curveball has produced a 51.1% whiff rate in the minors and 75.0% in the major leagues.

The sweeper is another pitch that's generated a lot of whiffs in Triple-A. It's more of a tight, late-breaking pitch, designed to get chases and whiffs against right-handed hitters. Right-handers are batting .077 with a .154 slug and a 45.5% whiff rate.

The one area of concern for Mena is if his fastball will play in the strike zone. His four-seamer has been hit hard, with a .545 average and a .909 slugging percentage against the pitch. Once he clears that hurdle, he projects as a middle-of-the-rotation arm. Even with that issue, he is still the safest bet to develop into a starting pitcher in the organization in the next three years.

OF Kristian Robinson (No. 38)

Robinson made steady progress in the Arizona Fall League and it's carried over to the 2025 season. His strikeout rate is down from 35.7% to 28.5% without sacrificing walks. His overall swinging strike rate has dropped nearly 3% from 16.0% to 13.3%, with his contact rate improving 8% from 59.8% to 67.6%.

At the same time, his ground ball rate has improved from nearly 50% to 45.7%. The ground balls have crept up a little bit in recent weeks, as it was at 40% at the start of the month. That aside, Robinson is doing exactly what he needs to do to make use of his best tool: raw power. In the fall league, his bat speed was measured in the 77-83 MPH range, which helps him produce high exit velocities up to 114 MPH.

All of these peripheral improvements have resulted in strong offensive numbers. Robinson has a .298 average with a .995 OPS, 17 extra-base hits, and seven homers in 124 at-bats. He's also drawing walks at a high rate, with 28 in 158 plate appearances. His .430 on-base percentage ranks third in the Texas League while his .995 OPS ranks first.

One notable change in his swing is the change of his timing mechanism from a leg kick to a toe tap. While it's unclear what the motivation behind this change is, it suggests perhaps it's improving his ability to be on time with his swing and improving his contact rate and batted ball quality.

Continued improvements with the ground ball and swing-and-miss numbers should result in a promotion to Triple-A Reno. Following the top tier of bats in the system, Robinson gives the Diamondbacks some upside with an outfielder who can work counts, handle all three positions, and provide some thump. He projects as a fourth outfielder behind Corbin Carroll, Alek Thomas, and Lourdes Gurriel Jr., with an arrival date of some point next season.

RHP Hayden Durke (NR)

The Diamondbacks drafted a string of college arms in 2023, with Durke getting the largest signing bonus ($350,000) of them all. In 2025, he's pitched extremely well, with a 1.00 ERA and 2.02 FIP in 13 outings, and has struck out 33 hitters in just 18 innings.

After struggling to throw strikes in 2024, he's made significant progress in that area of his game. He's been prone to bouts of wildness, often leading to those walks coming in bunches. While he's only walked hitters in five of his 13 appearances, he's walked multiple hitters in all of them and 11 in total.

When he's dialed in, he can command up to three "plus" quality pitches between a 94-98 MPH fastball, a big-breaking curve, and a sharp, depthy slider. He leads the Northwest League in strikeout rate, sitting at 48.5%, and the second-highest difference between strikeout and walk rate (K-BB%) at 32.4%. That level of swing-and-miss translates well when it comes to projecting potential back of the bullpen arms.

Durke's stuff is of major-league quality; the next step in his development as a reliever is eliminating those bouts of wildness. That will include improving his first-pitch strike rate from 41.2% and getting hitters down in the count early. He's very much in the same tier prospect as Justin Martinez, where once he makes significant progress on his one flaw, he'll be a major league reliever sooner rather than later.

In terms of bullpen arms in the Diamondbacks system, Kyle Amendt and Juan Morillo are at the top of the list. However, after those two, it's anyone's pick between Durke, Landon Sims, and Yordin Chalas for the next wave of arms to climb up the system.

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