A Starting pitcher
I took the easy way out on this one. I think the Mariners could deal from any one of Logan Gilbert, Bryce Miller or Bryan Woo. I think there is a higher likelihood they sign Ohtani than trading Logan Gilbert, but there is a slight possibility. Ultimately, I don't think they will deal a pitcher at the MLB Winter Meetings, as I think it is more likely that they deal one after all of the big-name pitchers have signed and the market gets thin.
I know I have proposed a lot of trade ideas of them dealing from starting pitcher for a solid young controllable bat, but I am not completely in support of trading from their starting pitching depth. I understand if they do it and get a young corner outfielder, or a young third or second baseman, but I think the trades are just so hard to work through. If it happens at the MLB Winter Meetings, I think it will be a team that is ready to contend and doesn't want to wait for the free agency market dry up and be hung out to dry. That team, in my opinion, would get aggressive and offer a package of players that the Mariners just couldn't refuse.