Here's the BA Blurb on him from the 2014 Handbook:
"The 6'5" Castro is a physical specimen with one of the most projectable bodies in the minors, and has the potential to be a front-half of the rotation starter. He has a lean, wiry build, a tapered waist and long limbs. He threw 91-92mph before signing, and last year sat 93-96 and touched 99. He throws from a low three-quarters arm slot and gets above average sink. His long stride and long arms give him good extension, and the ball explodes out of his hand. His velocity, sink angle and release distance should make him tough on right handed hitters. His arm slot allows him to turn over a change up with above-average potential, and he has a developing slider with sweepy action and pronounced lateral tilt. Increased weight and strength have helped his body control and strike-throwing ability and will continue to be a priority for his development for the lithe Castro."