Shohei Ohtani
Okay, okay...this one may be more in the realm of a pipe dream than the others, but Ohtani's presence on the trade market cannot be ignored. While signing Ohtani to a long-term deal is an extreme longshot given that it appears as though he strongly prefers to stay on the West Coast, Boston has the prospects to make a competitive offer for Shohei.
The trick, of course, is whether or not the Angels actually decide to trade him. At the moment, they are still talking with other teams about potential trade packages for Shohei. However, they aren't going to make any decisions about actually trading him until at least a couple days before the trade deadline and the Angels are actually playing pretty well right now. There is also a certain amount of skepticism that the Angels want to be known as the team that traded away a generational talent like Ohtani.
Tim Anderson
While acquiring an outfielder is a possibility especially if the Red Sox do end up trading Adam Duvall, acquiring an infielder seems more likely and Chicago's Tim Anderson fits here as a two-time All-Star. Anderson has looked like a shadow of his usual self in 2023 as he has seen his wRC+ drop 60 points this season, but he has been a 2.0 fWAR or better player the last five seasons.
Boston would have to do their due diligence with his physicals if they were going to make this move as has had some recent injury issues. However, the upside is huge here if Boston can get him turned around and he has a very reasonable club option for 2024 that the Red Sox could exercise if he plays well.
Michael Lorenzen
This is a funny one because Michael Lorenzen even being named an All-Star this season was basically because there was no one else on the Tigers was worthy other than the injured Eduardo Rodriguez. However, that doesn't mean that Lorenzen couldn't be an intriguing option for Boston at the trade deadline.
He is a pending free agent making a very reasonable $8.5 million this season. While his peripherals don't jump off the page, he has still posted a 3.49 ERA so far this season in 17 starts. He doesn't miss a lot of bats, but he throws a lot of strikes and has succeeded this season despite one of the worst groundball rates of his career. There is room for upside here and assuming Detroit's asking price is reasonable, Boston could do a lot worse than Lorenzen.