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Also in this series: 1-5, 6-10, 11-15, 21-25, 26-30, 31-35, 36-40.

20. Lewin Diaz | First Base | DOB: 9/96 | Bats: Left | Sign: Dominican

YEAR     LV      PA      AVG      OBP      SLG     HR    XBH     BB     SO
2014     DSL    174     .257     .385     .451      5     18     26     24

Lewin Diaz was the Twins' biggest ticket item from 2013 international spending, signing for $1.4 million out of the Dominican Republic as a 16-year-old. Baseball America referred to the 6-foot-4 first baseman's "big, lumbering body" and wrote that "his value is all in his bat." That player type normally doesn't interest the Twins, but Diaz made his pro debut last season in the Dominican Summer League and batted .257/.385/.451 with 18 extra-base hits and 26 walks in 43 games.

Rookie-ball numbers are to be taken with large grains of salt and the Dominican Summer League is even a step down from that in terms of competition, so Diaz's actual numbers there don't mean much. However, the fact that he hit a bunch of homers and doubles while walking more than he struck out is certainly a positive first impression by a 17-year-old. He was signed for his bat and so far his bat looks pretty good.

For some context his Isolated Power was 125 percent higher than the Dominican Summer League average and he drew 45 percent more walks than the DSL as a whole. When your body type is compared to guys like David Ortiz and Ryan Howard at age 16 you obviously need to hit a ton to make it to the big leagues, which Diaz will look to continue doing at rookie-ball in his American debut this year.

19. Chih-Wei Hu | Starter | DOB: 12/93 | Throws: Right | Sign: Taiwan

YEAR     LV      G     GS      ERA        IP       H     HR      SO     BB
2013     RK-    12      5     2.45      36.2      28      0      39      8
2014     RK+     3      3     1.69      16.0       7      0      16      2
         A-     10      9     2.29      55.0      40      0      48     13

Signed out of Taiwan for $220,000 in late 2012 as an 18-year-old, Chih-Wei Hu had a strong debut in the rookie-level Gulf Coast League in 2013 with a 2.45 ERA and 39/8 K/BB ratio in 37 innings. He began last season one level higher at rookie-level Elizabethton, but after just three impressive starts there the Twins decided to promote him to low Single-A. Hu didn't miss a beat, holding Midwest League hitters to a .201 batting average and zero homers in 55 innings.

Hu draws the most praise for his mature approach, strike-throwing ability, and quality changeup, but the 6-foot-1 right-hander is hardly a soft-tosser and can reach the mid-90s with his fastball at times. He has a 103/23 K/BB ratio in 108 career innings through age 20 and has yet to allow a home run in 420 plate appearances despite facing older competition in the vast majority of those matchups.

It's important to keep expectations in check for low-minors pitchers and Hu still needs to show that he can handle a full-season workload as a starter, but he's someone to keep an eye on this season and could rank much higher on this list next year. He was highly thought of as a prospect before signing, has fared very well against older competition at three different levels, and backs up the numbers with quality raw stuff.

18. Taylor Rogers | Starter | DOB: 12/90 | Throws: Left | Draft: 2012-11

YEAR     LV      G     GS      ERA        IP       H     HR      SO     BB
2012     RK+     6      6     1.80      30.0      20      2      39      5
         A-      9      4     2.70      33.1      33      5      35     12
2013     A-      3      3     7.20      10.0      14      1      10      4
         A+     22     21     2.55     130.2     119      5      83     32
2014     AA     24     24     3.29     145.0     150      4     113     37

Taylor Rogers went 13-18 with a 5.35 ERA in three seasons at the University of Kentucky, but the Twins picked him in the 11th round of the 2012 draft and now he's 26-16 with a 2.94 ERA in three seasons as a pro. His success has come despite mediocre strikeout rates, but that inability to miss bats against Single-A and Double-A hitters--and the lack of upside that suggests--is what keeps him from being considered a top prospect.

Last year at Double-A he posted a 3.29 ERA in 24 starts, but managed just 113 strikeouts in 145 innings for a rate below the Eastern League average. It wasn't all smoke and mirrors, though. Rogers had a good walk rate, allowed just four homers in 606 plate appearances, and induced lots of ground balls. And while he was much more effective against lefties than righties, the 6-foot-3 southpaw still held righties to a .367 slugging percentage with a 73/29 K/BB ratio.

Rogers was relatively young for Double-A at age 23 and his velocity has improved to the point that he regularly works in the low-90s, so he's certainly not without potential. Right now he projects as a back-of-the-rotation starter, but an uptick in strikeouts or improved control to go along with the strong ground-ball rates would give him mid-rotation upside. Either way, he's a candidate to reach the majors in 2015 and the Twins' decision-makers generally speak highly of him.

17. Adam Walker | Right Field | DOB: 10/91 | Bats: Right | Draft: 2012-3

YEAR     LV      PA      AVG      OBP      SLG     HR    XBH     BB     SO
2012     RK+    252     .250     .310     .496     14     25     19     76
2013     A-     553     .278     .319     .526     27     65     31    115
2014     A+     555     .246     .307     .436     25     45     44    156

Adam Walker's power potential is undeniable. He put up big college numbers at Jacksonville to get picked by the Twins in the third round of the 2012 draft, went deep 14 times in his 58-game debut at rookie-ball, and led his league in homers during each of his first two full seasons. Last year his 25 homers for Fort Myers led the Florida State League and no one else managed even 20 long balls. Walker can hit the ball over the fence.

Unfortunately his inability to control the strike zone stands out almost as much. He's struck out a lot and rarely walked dating back to college and as a pro he's whiffed 347 times in 319 games. That's a red flag, especially when he's already 23 years old and has yet to face competition above Single-A. Walker showed a bit more selectivity last year with 44 walks in 555 plate appearances, but that came with 156 strikeouts and led to a lowly .246 average and .307 on-base percentage.

Most high-strikeout sluggers in the majors didn't actually strike out a ton in the minors because striking out a ton in the minors usually leads to failing in the majors. Walker needs to cut down on his strikeouts or at least learn to draw walks at a much higher rate or his 30-homer power will be wasted. He's a good athlete with above-average speed for a corner outfielder and should be a plus defensively, so if the strike-zone control clicks at some point he has plenty of all-around upside.

16. Michael Tonkin | Reliever | DOB: 11/89 | Throws: Right | Draft: 2008-30

YEAR     LV      G     GS      ERA        IP       H     HR      SO     BB
2012     A-     22      0     1.38      39.0      29      1      53      9
         A+     22      0     2.97      30.1      24      2      44     11
2013     AA     22      0     2.22      24.1      21      0      30      8
         AAA    30      0     4.41      32.2      33      3      36      8
         MLB     9      0     0.79      11.1       9      0      10      3
2014     AAA    39      0     2.80      45.0      41      2      46     12
         MLB    25      0     4.74      19.0      23      2      16      6

After beginning his pro career as a 30th-round draft pick and mediocre starter prospect Michael Tonkin shifted to the bullpen full time in 2011 and has looked like a late-inning reliever prospect ever since. He's split each of the past two years between Rochester and Minnesota, posting a 3.48 ERA with 82 strikeouts in 78 innings at Triple-A and a 3.26 ERA with 26 strikeouts in 30 innings in the majors. At age 25 he's deserving of extended chance in the Twins' bullpen for 2015.

Tonkin is a sturdy 6-foot-7 with the velocity to match his size, averaging 94 miles per hour with his fastball in the majors. He also throws a sharp, mid-80s slider that has already proven to be a plus pitch against big-league hitters by generating swinging strikes and ground balls. He's allowed a total of just 13 homers in 278 innings between the minors and majors over the past four years, including no more than four homers in a season.

Tonkin has top-notch raw stuff, misses plenty of bats with his fastball-slider combo, and unlike lots of hard-throwing reliever prospects he actually throws strikes too. His career walk rate is a very reasonable 2.5 per nine innings, including 2.3 at Triple-A and 2.7 in the majors. By this time next year there's a decent chance Tonkin will be entrenched as Glen Perkins' primary setup man and will have his own identity rather than being known as Jason Kubel's brother-in-law.

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