The roster for next month’s ambitious Quintet Ultra continues to fill, and four new team participants have been booked, along with three “superfight singles” matches. Featuring a unique 5-on-5 team grappling concept, Quintet Ultra takes place Dec. 12 at Red Rock Casino in Las Vegas and streams live on UFC Fight Pass. While the events often feature big-name mixed martial artists, Quintet Ultra will see teams representing the biggest promotions in MMA history face off with Team UFC, Team Strikeforce, Team WEC and Team PRIDE. MMA Junkie today learned from Quintet officials that four new fighters have agreed to compete at the event, with current welterweight contender Gilbert Burns joining team UFC, former light heavyweight champion Muhammed Lawal added to Team Strikeforce, 15-year veteran Cub Swanson repping Team WEC and submission ace Gregor Gracie joining Team PRIDE. Quintet founder, MMA legend Kazushi Sakuraba, said he was thrilled to announce all of the additions, but as a former Gracie hunter was now happy to have a member of MMA’s founding family on his side.