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PEORIA, Ariz. -- Luis Castillo did not begin throwing a new pitch this offseason, oddly making him the glaring outlier among the Mariners’ starting staff.

Pitchers arriving at Spring Training with a new weapon is as cliché as a guy showing up in “the best shape of his life.” Yet for a rotation that could be among the American League’s best, with established arms possessing plus stuff, the breadth of the adjustments is unique.

“I've been in a rotation with Zack Greinke, and he's always messing around and creating new pitches,” Robbie Ray said. “But I’ve never really seen four-fifths of the rotation [do it].”

Castillo aside, Ray, Logan Gilbert, George Kirby, Marco Gonzales and Chris Flexen -- who’s on the outside but is being stretched out -- all showed up with a new toy to tinker with.

Here’s a look at what each guy added and why:

Robbie Ray
Pitch: Splitter
Purpose: He wanted to give hitters a different look from his fastball/slider combo.

“I think it just gives me something that's just a different dynamic to my game,” Ray said. “Everything is kind of hard and goes to my glove side. Ideally it's something that's a little bit softer and goes to my arm side. So I think it just kind of adds another dynamic.”

Ray has been a two-pitch pitcher for most of his career, but he added a two-seam fastball mid-start last June in Houston, which became a big weapon for him. In 15 starts against the AL West, he had a 4.16 ERA and opposing hitters had a .264/.323/.492 (.816 OPS) slash line with 18 homers against him, so giving the familiar faces a new look could be part of the logic.

Logan Gilbert
Pitch: Split-changeup
Purpose: He wanted an offspeed pitch that he could trust more.

“I've always tried the changeup and just kind of struggled with it, just wasn't natural for me,” Gilbert said. “So I’m just trying to find basically a variation of a splitter that I can throw like a fastball.”

Because Gilbert has such large hands and huge extension down the mound, the club believes the pitch’s late-breaking movement will be conducive to his profile. 

“I kind of thought about it last year and then threw it off some people, and they thought it was a good idea, too,” Gilbert said. “I talked to coaches here and then a couple players, and just kind of brainstorming. I'm still developing it, just trying to see what it looks like against hitters.”

George Kirby
Pitch: Splitter
Purpose: He wanted something that could induce weak contact.

Last year, only Shohei Ohtani and Chris Bassitt had a more diverse repertoire than Kirby, who threw six different pitches, each one amounting to at least 8 percent of his overall usage. And for a player whose ability to manipulate grips is among the best that his peers have ever seen, why not add a seventh?

“I just want something … more like a heater,” Kirby said. “A little more deception, something [with] a little more depth to possibly [induce] a little more swing-and-misses, some weaker contact. ... I kind of just throw it like a heater, and it just falls off the table more vertical. And then I still have my changeup, too, which is a little more horizontal.”

Ideally, Kirby said, his split would have an 8-10 mph dropoff from his fastball.

Marco Gonzales
Pitch: Slider
Purpose: He wanted something with more movement than his cutter.

“I unintentionally was throwing sliders last year,” Gonzales said. “Unintentionally, intentionally. I was trying to make my cutter bigger to lefties and have it kind of run off the plate. This year, I just gave it its own focused path, its own intention, and started calling it a slider and working on it as a slider.”

Opposing hitters batted .321 and slugged .547 against Gonzales' cutter last year, per Statcast, which factored into the decision. 

“Talking with the pitching coaches, the numbers look good on it,” Gonzales said. “So we decided to let it rip. Instead of thinking big cutter, [the slider] is more intentional now.”

Chris Flexen
Pitch: Slider
Purpose: He needed a breaking ball.

“The curveball for me last year was just a far-below-average pitch,” Flexen said. “I just couldn't figure it out. I had a good one in '21. I don't think I'm going to completely get rid of it, but I needed a breaking ball. And when I started working on the slider last year, I had good results with it. I felt good throwing it. So that was the pitch that I wanted to continue to stick with.”

Flexen’s curve usage dropped from 15.3 percent in 2021 to 3.6 percent in '22, when opposing hitters had a .615 batting average and 1.308 slugging percentage against it. The slider has shown promise this spring.

“Maybe as a starter, if I'm in the rotation or wherever, using the curveball is just kind of a show-me pitch just to say, 'Hey, I still have it,'” Flexen said. “But I needed a breaking ball. It was nonexistent for me last year.”