Usually it's easy to dismiss first-half/second-half splits, but in the case of Castillo, it's hard to overlook his superb second half, especially when there's an easy explanation for his improvement. Before the All-Star break, Castillo had a 5.49 ERA, 1.65 HR/9, 21.5 K% and 7.9 BB% over 103.1 innings. In 66.1 innings after the break, Castillo turned in a 2.44 ERA, 1.22 HR/9, 26.3 K% and 5.3 BB%. The difference? Every one of Castillo's pitches recovered most of the velocity that he had in 2017 but had lost during the first half of 2018. Take his four-seamer as an example -- in September 2017 it clocked in at 97.3 mph, but in April it was down to 95.4 mph, and stayed down at that level until late July/early August, when it got back up to 96.6 mph (velocity readings courtesy of Baseball Savant). Even with the strong second half, Castillo didn't earn his NFBC ADP of 103.3, but he might exceed that in 2019 if he maintains his second-half velocity.

The Reds had been trying to develop a frontline starter to fill Johnny Cueto's shoes for a couple years, but it came to them in the unlikely form of Castillo, who was involved two trades and one rescinded trade before reaching the majors. He debuted after just 94.1 innings at Double-A and zero experience at Triple-A. Teams didn't figure him out as the year went on -- his ERA actually improved each month from July to September. Castillo was particularly dominant away from Great American Ball Park (2.84 ERA in 44.1 innings). His .247 BABIP, which would have been fifth lowest among qualified starters, will clearly regress. While we can't bank on a repeat of his rookie ratios, he should still be very effective in year two. He throws three pitches -- a fastball that averages 97.5 mph and tops out around 99-100 mph, an out-of-this world changeup and a rapidly improving slider. He has the stuff, command and size (6-foot-2, 190 pounds) to pitch atop a rotation.

Best known for being traded to San Diego and then sheepishly traded back to Miami when Colin Rea's elbow gave out after the trade, Castillo has emerged as one of the best prospects in a desolate Marlins system. He sports an 80-grade fastball with an above-average changeup and two breaking balls that are works in progress, but there is still plenty of time for refinement in the upper levels of the minors. That incomplete repertoire was still more than enough to dominate Florida State League hitters. The lack of strikeouts despite cheddar that touches triple digits illustrates his lack of a consistent out pitch, so he will need to continue to improve those offerings if he hopes to have success as a starter at Double-A and Triple-A. He is relatively new to starting, having worked exclusively as a reliever from 2012 to 2014, so becoming more adept at sequencing will also help him miss more bats. This is an arm that could take a big jump up prospect lists this year, especially now that he's in a Reds' system in the middle of a complete rebuild.