The 21-year-old native of Canada was previously selected by the Florida Panthers with the 114th overall selection in the 2016 NHL Entry Level Draft.
The son of former Panther forward, Cory Stillman, had a relatively successful career in the OHL for the Oshawa Generals and Hamilton Bulldogs.
While participating in 195 OHL contests, Riley Stillman produced 88 total points as well as a plus rating on defense. The former alternate captain of the Oshawa Generals spent the majority of the 2018-19 pro-hockey season with the Springfield Thunderbirds of the American Hockey League.