Mastroianni has seen more playing time recently, as it marked his fifth start in the last week after playing sparingly throughout most of June.
He's taken advantage of it by hitting .429 with six stolen bases dating back to Saturday's doubleheader against the Royals.
"He's pretty fun to watch," Twins manager Ron Gardenhire said. "He's very entertaining on the basepaths. He looks for openings, he can take advantage, he can outrun some things. I like to see him in there."
Stealing bases is nothing new for Mastroianni, who stole as many as 70 in a season as a Minor Leaguer while in the Blue Jays organization. He has eight stolen bases in nine tries this year after stealing three bases against the Tigers on Thursday.
"I take a lot of pride in it," Mastroianni said. "Speed has always been a big part of my game. I've always been a pretty good basestealer throughout my career in the Minor Leagues. I've learned a lot over the years."
Mastroianni said he studies the pitcher and catcher every game whether or not he's playing to try to give pointers to his teammates about whether they'll be able to steal. He added he stands in the same spot in the dugout every game to get the best angle to watch the pitcher.
"Just because you're on the bench doesn't mean you're useless," Mastroianni said. "It's my way of trying to help the team even when I'm not playing."