The Mets designated Slater for assignment Tuesday.
The transaction frees a spot on the 26-man active roster and 40-man roster for left-hander Anderson Severino, whose contract was selected from Triple-A Syracuse. Slater was released by the Tigers during spring training and has now been designated for assignment twice in less than a month. He'll likely become a free agent after clearing waivers. Slater has slashed .209/.286/.233 across 49 plate appearances between stops with the Marlins and Mets this season.