13. Hector Olivera: Six Years, $62.5 million ($28 million signing bonus), 2015
The only reason the Olivera contract doesn't rank higher is because the Dodgers were able to get him excommunicated from their farm before things went truly sour.
Olivera was mostly an Atlanta Brave after signing a March 2015 deal to defect to MLB, but the Dodgers did have to pay his massive signing bonus ... and, in exchange, received six games in Double-A and seven in Triple-A before he was part of a three-team whirlwind that sent Mat Latos, Bronson Arroyo, Alex Wood, Michael Morse and others to help make over the '15 Dodgers.
Olivera, of course, racked up -0.3 WAR during his MLB career and was suspended 82 games the next season under the league's domestic violence policy. He retired at 32 after a brief stint with the independent Sugar Land Skeeters. Horrendous, by every measure.