SM Entertainment’s 30th-anniversary celebration concert, SMTOWN Live in Seoul, brought together some of the company’s biggest stars for a two-day spectacle. Among the performances, Red Velvet’s Seulgi teamed up with RIIZE’s Sungchan for a special rendition of Seulgi’s B-side track, “Bad Boy, Sad Girl.” | @hi_sseulgi/Instagram | @riize_official/Instagram The original track, which features rapper BE’O,…