Mason returns after spending part of last season on the Bears practice squad. He re-signed with the team Jan. 4 and remained on the roster until being waived May 25. Mason entered the NFL in 2015 as an undrafted free agent with the Broncos, but he did not play in any regular-season games.
Williams appeared in 41 games with 21 starts over five seasons with the Panthers from 2009-14. He played in all 16 games with 11 starts in 2010 before missing the entire 2011 season with a broken ankle. He appeared in 16 games with nine starts in 2012, but tore his ACL in the 2013 season opener.