Luckily, Armstrong already dealt with aging struggles when his fastball velocity dipped in 2024, dropping a full tick. He had one of the worst seasons of his career as a result. At the end of that season, he began throwing a sweeper for the first time since 2018, but it was too little too late. In 2025, he changed his pitch usage, dropping his slurve entirely and using the sweeper more often so that he used all four pitches at close to an even split. This kept hitters guessing and allowed his two fastballs to regain effectiveness without the higher velo. His sweeper and 4-seam fastball are legitimately great pitches, with both generating a whiff rate over 33% . With the youth of the M’s bullpen, Armstrong would make a strong veteran leverage arm at an affordable price. That makes him a great target for the Mariners.
There are other interesting names like Tyler Kinley, Seranthony Dominguez, and Caleb Theilbar, who would all likely be more affordable free agents. However, they carry more significant risks. Theilbar is 38, and although he seemed to have figured something out last season, the drop-off risk due to age is high. Still, after posting a 2.64 ERA, 3.00 FIP, and 0.88 WHIP over 58 innings in 2025 due to changes in pitch usage, leaning more on his slider and curveball, he is tempting. But at 38, it is hard to count on sustainability. He is also a lefty, and the M’s may not need another after acquiring Ferrer. Because he is older, he would likely be affordable and willing to sign a one-year deal if the Mariners wanted to take a chance.
Seranthony Dominguez and Tyler Kinley are in their early thirties with some very tempting traits, but both have big problems with command, with each of them walking over 10% of the batters they face. They also have below average fastballs, and rely on their breaking and off-speed pitches to get batters out. Last season, Dominguez had an ERA of 3.16, 3.47 FIP, and a 1.28 WHIP over 62.2 innings. Kinley had an ERA of 3.96, 3.69 FIP, and 1.18 WHIP in 72.2 innings. Dominguez has an excellent strikeout rate of 30.3%, and does a good job of limiting hard contact, but has one of the worst walk rates in the MLB. Kinley has a devastating slider that he uses 64% of the time but still doesn’t get a ton of strikeouts. Instead, his value lies in his ability to induce pop-ups and weak contact. He does have a changeup that performs really well when he throws it, but he uses it just 1% of the time. Both of these guys seem like great candidates for the Mariners pitching lab, but since they would cost real money to sign, it may deter them from taking a shot.
Final Thoughts
The Mariners made a bold first move by acquiring Jose Ferrer, a young left-hander with elite underlying metrics and significant upside. But this trade alone will not complete the bullpen overhaul the front office has prioritized. With several strong veteran relievers still available, including Tyler Rogers and Shawn Armstrong, the Mariners have a chance to add experience and stability to complement their young arms. Whether they choose the proven upside of Rogers, the affordability of Armstrong, or a calculated gamble on a riskier arm, their next decision will shape whether this bullpen becomes merely improved or truly elite.