Mattison is a 6-foot-2, 195-pound right-handed pitcher with a history of missing bats. Before transferring to Kentucky, he spent two seasons at Grand Canyon, where he became one of the program's most accomplished young pitchers. As a freshman, Mattison threw Grand Canyon's first no-hitter in 42 years, striking out 10 batters against Sacramento State. He earned national recognition while finishing the season with a 12.5 K/9 rate and multiple weekly honors.

In 2025, Mattison continued to show swing-and-miss ability, leading the team with 41 strikeouts in just 33 1/3 innings while earning WAC Pitcher of the Week honors after throwing five shutout innings against Vanderbilt. The move to the SEC level at Kentucky proved more challenging.

Mattison made 14 appearances (six starts) and posted an 8.10 ERA with a 1.53 WHIP. However, some underlying numbers suggest there could be more upside. His 6.33 FIP and .337 BABIP indicate some bad luck, while his strikeout rate remained above 20%. The Twins are betting that their pitching development staff can help Mattison recapture the dominant stuff he showed earlier in his career.