I swear I’ve never seen Kim Bum Soo go by BSK... is it something he did for this show or...?

smtm6 semifinals 

nucksal (ft kim bum soo) vs junoflo (ft changmo & kim hyo eun) woo won jae (ft suran & YDG) vs jo woo chan (ft sik-k) hanhae (ft shin yong jae) vs hangzoo (ft swings)