#3 - The Marcell Ozuna Trade
The Cardinals needed a big bat prior to the 2018 season, and Marcell Ozuna was coming off of a .924 OPS season along with a Gold Glove for the Miami Marlins. After striking out on the Giancarlo Stanton trade, St. Louis acquired Ozuna from the Marlins for a package of prospects headlined by two of their lower-ranked pitching prospects, Sandy Alcantara and Zac Gallen.
Yeah, that went about as bad as it sounds.
Ozuna was pretty good for St. Louis over his two seasons there, posting a .777 OPS across 278 games played, but was allowed to leave in free agency following the 2018 season.
On the other side of this trade, Alcantara is coming off a 14-9 season where his ERA was 2.28 over an MLB-high 228.2 innings pitched and a Cy Young award at age-26. Alcantara is easily one of the best pitchers in all of baseball, in his prime, and on an extremely team-friendly extension for the foreseeable future.
Gallen was a Cy Young candidate himself this last season for the Arizona Diamondbacks. He went 12-4 with a 2.54 ERA over 184 innings of work and has also emerged as a top stater in today's game. Also entering his age-27 season, the Cardinals effectively gave up two young, in their prime aces for a two-year rental of Ozuna.
What really hurts is that if the Cardinals' had these two guys, they are easily the World Series favorites this year. Even with just one of them, they likely are neck and neck with the best teams in the league, and still would have so many assets to deal if they desired. You can check out a deeper breakdown of the Ozuna trade here.