"I build them up in BP," said manager Mike Redmond, who pitched to Mahoney. "That's what I do. He's a big, strong guy."
Mahoney on Wednesday was reinstated from the 15-day disabled list, where he had been out with an intercostal strain. The first baseman, who also may play some corner outfield, is replacing catcher Kyle Skipworth, who was optioned after Wednesday's 8-2 win over Washington.
Mahoney showed some power in Spring Training, belting three home runs while driving in eight in 30 at-bats before he was sidelined.
In four rehab-assignment games for Class A Jupiter, Mahoney hit .438 (7-for-16) with one home run.
"I was feeling good down there, and [the Marlins] had a need," Mahoney said. "That's what I'm here for, to help this team win any way I can."
Mahoney was an option off the bench on Wednesday night, and Redmond is trying to figure out when to use him. Greg Dobbs has been effective at first base since Casey Kotchman strained his left hamstring in the second game of the season.
"[Mahoney] gives us another left-handed bat," Redmond said. "We've got to figure out when we will get him in there. He's a guy with power potential in the batting order. Hopefully, he will be a boost to our lineup."
A year ago, Mahoney made his big league debut with the Orioles. He appeared in two games and was hitless in four at-bats.
Joe Frisaro is a reporter for MLB.com. He writes a blog, called The Fish Pond. Follow him on Twitter