The New York Yankees signed Castillo as an international free agent in December 2014. He was assigned to the Double-A Somerset Patriots to begin the 2021 season.
On July 26, 2021, the Yankees traded Castillo along with Hoy Park to the Pittsburgh Pirates for Clay Holmes.[1] Castillo slashed .278/.355/.487 with 19 home runs, 55 runs batted in (RBIs), and nine stolen bases in 105 games split between the Double-A Altoona Curve, Triple-A Indianapolis Indians and Somerset. The Pirates added Castillo to their 40-man roster after the 2021 season.[2]
On April 4, 2022, it was announced that Castillo had made the Pirates’ Opening Day roster.[3] On April 9, Castillo collected his first career hit, lacing a pinch-hit double off of St. Louis Cardinals reliever T. J. McFarland.[4] He played in 96 games in his rookie campaign, hitting .206/.251/.382 with 11 home runs and 29 RBIs. He was designated for assignment on December 20, 2022.[5]
On December 23, 2022, Castillo was traded to the Arizona Diamondbacks in exchange for pitcher Scott Randall.[6] Castillo was optioned to the Triple-A Reno Aces to begin the 2023 season.[7] He spent almost the entire season in Reno, appearing in one game for Arizona, and hit .313/.431/.410 with 3 home runs, 72 RBI, and 13 stolen bases across 124 games. The Diamondbacks designated Castillo for assignment on December 22.[8]
On January 5, 2024, Castillo was claimed off waivers by the New York Mets.[9] However, on January 12, he was designated for assignment following the signing of Sean Manaea.[10] On January 19, Castillo was again claimed off waivers, this time by the New York Yankees,[11] who designated him for assignment themselves on January 29.[12] He was then claimed by the Philadelphia Phillies on February 5, [13] who designated him for assignment on February 14.[14] On February 16, Castillo was again claimed off waivers, this time by the Baltimore Orioles,[15] who designated him for assignment two days later.[16] He cleared waivers and was sent outright to the Triple–A Norfolk Tides on February 20.[17] In three games for Norfolk, Castillo went 4–for–13 (.308) with no home runs, no RBI, and three walks.