The 19-year-old forward was selected in the first round (No. 30) of the 2017 NHL Draft. Playing for Jokerit last season, he set Kontinental Hockey League records for under-19 players with 19 goals and 36 points, surpassing the 17 goals and 32 points Evgeny Kuznetsov had in 2010-11.
Tolvanen also had six points (one goal, five assists) in six games for Finland at the 2018 IIHF World Junior Championship, and led Finland with nine points (three goals, six assists) at the 2018 PyeongChang Olympics, making the all-star team.
He made his NHL debut against the Buffalo Sabres on March 31, and had three shots in three games.
Tolvanen said it didn't take him long to learn that he had to adjust to the speed and physicality of the NHL.
"It's way faster and it's more physical than the KHL was," Tolvanen said. "You just have to be ready every time you touch the puck. If you make a mistake, it's going to come back."