5. The Jake Marisnick trade
It's easy to forget that Jake Marisnick was on the Chicago Cubs because he was traded after four months of his services. Realistically, Marisnick is a replacement-level player that provides good defense but a mediocre bat on a good day. This is why the Padres sent one Single-A pitching prospect named Anderson Espinoza to the Cubs. But Espinoza elected free agency after getting outrighted off the 40-man roster.
Espinoza signed back with the Padres after, meaning the Cubs essentially got next to nothing for this deal. But hey, the Cubs were in a selling-all-assets mode so again I don't blame the front office for this deal or it being a failure.
Padres get: Jake Marisnick
Cubs get: Anderson Espinoza