Mittelstadt has played left wing on what's been the most productive U.S. line so far, with center Logan Brown (Ottawa Senators) and right wing Kailer Yamamoto (Edmonton Oilers).
"Me, [Brown and Yamamoto] made a lot of quick little passes and were moving and trying to find some open areas, and I think that's what we do really well together and that's when I'm at my best," Mittelstadt said.
Mittelstadt's inspired play is a remnant of last year's Summer Showcase, when he was an early cut and then wasn't invited to the final selection camp for the 2017 WJC in December.
"Obviously it was tough," he said. "You want to make it and be here as long as you can. At the same time it was a good learning lesson."
Mittelstadt had a strong 2016-17 with Eden Prairie (Minn.) High School and Green Bay of the United States Hockey League. He averaged 2.56 points in 25 high school games and led the USHL with 1.25 points in 24 games. The Sabres chose him with the eighth pick of the 2017 NHL Draft.
Despite not being part of the U.S. team that won the gold medal at the 2017 World Juniors, Mittelstadt watched as much of the tournament as he could.
"Even though I wasn't there I was still cheering for them," he said. "I had good buddies on the team, lot of Minnesota guys on the team."
Now he's back for this year's Summer Showcase more comfortable and feeling like he can display the full scope of his talent.