Castillo signed a contract with Mexican League club Diablos Rojos del Mexico on March 25, Francys Romero of BeisbolFR.com reports.
Castillo was briefly up in the big leagues with Seattle in 2025, making two starts and logging a 7.71 ERA and 2.71 WHIP in seven innings. Now 31 years old and pitching outside of affiliated ball, Castillo could face an uphill battle to make it back to the majors.