But when they're ready to join the Devils, Fitzgerald said he believes they will complement the young players they already have, including centers Jack Hughes, a 19-year-old who was the No. 1 pick in the 2019 NHL Draft, and Nico Hischier, a 21-year-old who was the No. 1 selection at the 2017 NHL Draft.
Holtz (6-foot, 192 pounds) led under-18 skaters in the Swedish Hockey League with 16 points (nine goals, seven assists) while averaging 12:53 of ice time in 35 games in 2019-20. After being promoted to Djurgarden's top line, the right wing has one goal in three games to begin 2020-21.
"It's hard to score goals in [the NHL], and that's what this kid projects to do," Fitzgerald said. "Then, on top of it, you get a little giddy when you get a chance to think about the centers that he's going to be able to play with."
Having played for Sweden against Hughes and the United States in the 2019 Under-18 World Championships, Holtz said he would love the opportunity play alongside him.
"It's really exciting," Holtz said. "He's an incredible player, so I'm really looking forward [to it]."
Mercer, who was selected with the first-round pick the Devils acquired from the Arizona Coyotes as part of the trade for forward Taylor Hall on Dec. 16, 2019, can play center or wing. The 18-year-old scored 60 points (24 goals, 36 assists) in 42 games in 2019-20, including 18 points (six goals, 12 assists) in 16 games for Chicoutimi after being acquired in a trade with Drummondville on Jan. 6.
Fitzgerald said he envisions Mercer (6-0, 180) possibly slotting in behind Hughes and Hischier as New Jersey's third-line center. Mercer said he tries to model his two-way game after Boston Bruins center Patrice Bergeron and is excited about the Devils' future.
"They have a lot of young prospects and a young team there now that has some high-end talent from the last couple years, and I think the future is going to be bright for them," Mercer said. "Right now, I think there's a lot of development throughout these young guys coming in, and all I can see is when we all turn [out] at our highest potential, there's going to be great things happening."