The Opening Day bullpen
RP Yohan Ramirez
RP Will Vest
RP Brandon Brennan
RP Anthony Misiewicz
RP Keynan Middleton
SP/RP Kendall Graveman
RP Rafael Montero
The bullpen will be decided at spring training as there are now a few arms who will certainly make the seven-man pen, but there are plenty of pitchers who will be fighting for the last few spots. Ramirez and Misiweicz looked excellent last year in the shortened season and will be a part of the opening day bullpen, and Kendall Graveman looked excellent when he switched over to a relief role last year.
Middleton and Montero should be 100%’ers to make the bullpen as well as they were just signed and traded for. The last two spots belong to Will Vest, who the Mariners drafted in the Rule 5 draft, and Brandon Brennan, who the Mariners took in the 2018 Rule 5 draft.
Vest would be in jeopardy of being sent back to the Detroit Tigers, but with the Mariners still rebuilding they will want to see him in the majors for at least a few outings, so he will be in the opening day pen.
There are plenty of options for the final spot, but Brandon Brennan has pitched very well when he has been healthy and should be the last man in. If there are injuries or players traded Joey Gerber, Sam Delaplane, and Andres Munoz (When he finishes recovering from Tommy John surgery) should be the first ones to get the call, and recent waiver claims Robert Dugger, Casey Sadler, and Domingo Tapia are in jeopardy of being cut.