Mikkola, 22, spent the 2017-18 season with Tappara of Finland's SM-Liiga, posting two goals and nine assists (11 points) and a plus-11 rating in 50 regular-season games. Mikkola recorded the League's best plus/minus rating (+9) in the postseason and helped his club capture a silver medal.
Overall, the Kiiminki native has dressed in 171 career SM-Liiga games, recording 36 points (nine goals, 27 assists) and 169 penalty minutes.
Mikkola also represented his country in international play, where he captured a gold medal with Finland at the 2016 U-20 World Junior Championship.
Mikkola was originally drafted by the Blues in the fifth round (No. 127 overall) in the 2015 NHL Draft.
