2B Edouard Julien
A second baseman may be the last thing the Cardinals need, especially after Nolan Gorman's recent tear. However, Edouard Julien provides a bit of a different look than Gorman. Both are left-handed batters, but Julien has a greater propensity to draw walks (12.4% this year alone), and he doesn't chase nearly as often as Nolan Gorman does. For as improved as Gorman's defense has been, Julien's has graded out positively at second base this year.
The addition of Edouard Julien would likely supplant either Brandon Crawford or Matt Carpenter. While those two veterans have provided leadership that can't be quantified, their on-field performances have left plenty to be desired. Carpenter has a 55 OPS+ in 53 at-bats, and Crawford's 34 OPS+ is somehow worse. Neither has been strong defensively.
Julien is hitting better against left-handed pitchers this year (.701 OPS against lefties vs .673 against righties), but he has typically been better against right-handed pitchers. Most of his power is done via opposite-field hits, but he generally does a good job of spreading the ball around.
Julien has played first base, but it's been sparse. He's only 25, and the projections still expect him to be a 3.0-4.0 WAR player over the next 5 seasons. He's under team control for 4 more years after 2024, and his demotion is a bit questionable given his league-average bat and plus defense at second base. It doesn't seem like the Twins want to trade him, but it's wholly possible still.
The Cardinals would have to be comfortable giving up some pitching prospects to land Julien. He also doesn't quite have a clear role on this team so long as Nolan Gorman is starting at second base. But, he's demoted, and he's a decent player, so why not try?