An honor roll student, Mullen was named first-team All-County as a senior and compiled 112 career tackles.

[1] Mullen received several scholarship offers after high school, including from Indiana, Nebraska, and Pittsburgh.

[1] Following the season Mullen was named honorable mention All-Big Ten, first-team The Athletic Freshman All-American, and Indiana's defensive newcomer of the year.

[1] As a sophomore in 2020, Mullen made 38 tackles, 3.5 sacks, three interceptions, and four pass breakups and was named first-team All-American at the end of the season.

[11] His cousin, Lamar Jackson, is a starting quarterback for the Baltimore Ravens and was named NFL MVP.