On February 16, 2012, Castillo signed with the Arizona Diamondbacks as an international free agent.[1] He made his professional debut with the Dominican Summer League Diamondbacks, recording an 0–9 record and 4.48 ERA in 14 starts. He returned to the team the following season and went 4–4 with a 3.58 ERA in 14 starts. For the 2014 season, Castillo played for the rookie-level AZL Diamondbacks, posting a 3–3 record and 4.40 ERA in 15 appearances. The next season, Castillo recorded a 1.83 ERA in 11 games with the team. In 2016, he played for the rookie-level Missoula Osprey, posting an 0–3 record and 4.04 ERA in 19 games. For the 2017 season, Castillo played for the Low-A Hillsboro Hops, registering a 2.91 ERA with 35 strikeouts in 34.0 innings of work. He split the 2018 season between the Single-A Kane County Cougars, Hillsboro, and Missoula, accumulating a 2.41 ERA in 24 appearances between the three teams. In 2019, Castillo played tor the High-A Visalia Rawhide, recording a 9–0 record and 3.81 ERA in 43 appearances.[2]
Castillo did not play in a game in 2020 due to the cancellation of the minor league season because of the COVID-19 pandemic.[3] He was assigned to the Double-A Amarillo Sod Poodles to begin the 2021 season before receiving a promotion to the Triple-A Reno Aces in June.[4] Castillo finished the year with a cumulative 4.72 ERA in 29 appearances between the two affiliates. He elected minor league free agency following the season on November 7, 2021.[5]
Detroit Tigers
On February 1, 2022, Castillo signed a minor league contract with the Detroit Tigers organization.[6] He was assigned to the Triple-A Toledo Mud Hens to begin the season.[7] On August 6, 2022, the Tigers selected Castillo's contract and he made his major league debut that night.[8] On November 10, Castillo was removed from the 40-man roster and sent outright to the Triple–A Toledo; he elected free agency the same day.[9][10]
