Mastroianni appeared in 114 Major League games for the Twins from 2012-14, and spent all of last year in the International League with Triple-A Lehigh Valley and Syracuse. He hit .257 with 25 stolen bases in 29 attempts over 112 games.
Tovar, 24, has spent his entire career in the Mets' organization and has appeared in nine Major League games. Boshers, a former fourth-round pick of the Angels, last appeared in the Majors with Anaheim in 2013.
Kintzler, 31, has appeared in at least seven Major League games in each of the last six seasons with the Brewers, including 135 from 2013-14.