GOODYEAR, Ariz. -- For much of last season, Luis Castillo was firmly in the conversation for the American League Cy Young Award. A beacon of consistency who never missed a start. A workhorse who navigated early jams and somehow cleared the seventh inning. A strikeout artist who didn’t need data to tell him what worked and didn’t.

Until that fateful final week.

In his final two starts, against Houston and the loss to Texas that officially eliminated Seattle from postseason contention, Castillo was as far from himself as ever, surrendering nine runs, six walks and five of his 13 hits for extra bases. He was hardly the only player that shouldered the blame for Seattle’s shortcomings, but given his production to that point, it was confounding.

“For me, the most important thing ending the year was that we were all healthy,” Castillo said recently through an interpreter. “Like I said, things don't always go the way you want. But the best thing for me was that [our] rotation is still healthy.”

It all paved the way for 2024, which began for “La Piedra” on Monday, when he was on the mound again making his Cactus League debut. Castillo carved through his former team for two hitless innings, with one walk and one strikeout as part of a 2-0 win over the Reds at Goodyear Ballpark.

For an established arm who grows slower into his velocity than most and who utilizes Spring Training to regain his feel rather than install offseason adjustments, the radar gun was telling. Castillo fired 96 mph fastballs in the first inning, a significant rise compared to last year, when he was in the high-80s.

“That was a surprise for me,” Castillo said, “because not every year that you come in and you get all that juice right away.”

Does that reveal to him anything?

“It's telling me that I'm healthy,” Castillo said. “We're going to continue to be in the same routine, and hopefully that velocity will keep going up.”

The context of Castillo’s velocity might’ve been an intrigue, but there’s nothing surprising about that four-seam heater, which is among the game’s most elite. Last year, it held hitters to a .165 batting average and .384 slugging percentage, per Statcast, while generating a 33% whiff rate, an MLB-best among starters.

But it’s the re-tooling of his arsenal since joining the Mariners at the 2022 Trade Deadline that has been the most fascinating component to his game.

Castillo blossomed into a two-time All-Star in Cincinnati with a sinker/changeup combination being his most used, with the offspeed pitch being among the game’s best and one he often threw more than any other. In Seattle, thanks to consultations from the Mariners’ pitching braintrust, he’s turned to a four-seamer/slider composite.

The organization’s pitch to do so -- no pun intended -- was far more simple than spewing out data, and once Castillo installed it, things felt right.

“You could say he’s a little bit more old school,” Mariners manager Scott Servais said. “There are a few guys still running around like that, but not many.”

That type of communication has been one of the big reasons that Castillo has felt at home in Seattle, which in itself has been one of the big reasons he signed a five-year, $108 million extension one month after the trade. The Mariners maintained that open line this offseason, with Servais and pitching coach Pete Woodworth visiting their ace for a fishing trip in the Dominican Republic.

“It's the first time that's ever happened to me in my career, but from now on, they're always welcome in the house,” Castillo said. “I think the most beautiful thing and important thing was that it showed me that I'm always on their mind, that they're thinking of me.”

Castillo wound up finishing fifth in the AL Cy Young vote last season, the highest of his career -- and he makes it no secret that he intends to win the honor some day. It was probably going to be difficult for him to pass the eventual winner, Gerrit Cole, anyway, but starts like his final two -- particularly at that time of year -- are tough to overcome.

“It's a little frustrating the way it ended, but I think that's a little motivation for us to know the way it ended,” Castillo said. “Sometimes, things that aren't for us don't happen for us. But I think this year, hopefully the results will come our way and we're able to take this team really far.”