Young Thug has elevated mumbling to an art form, and his often indiscernible, melodic flows set him apart as one of today’s most innovative rappers. Controversy follows the young MC, who became embroiled in a beef between his mentors, Birdman and Lil Wayne, earlier this year. Lil Wayne objected when Young Thug originally announced that he would call his April mixtape Carter 6. The title choice seemed particularly trollish considering that Lil Wayne and Birdman were at odds over the release date of Lil Wayne’s Tha Carter V on Birdman’s Cash Money Records. (Tha Carter V never actually came out.) Thug acquiesced and renamed his tape Barter 6. When it dropped, the project was an instant hit among fans and music critics, and proved to be a testament to the rapper’s unique gift for weaving melodies from unusual cadences and seemingly discordant vocal flourishes. He further developed Barter’s stripped down aesthetic on his subsequent tape, September’s Slime Season, which balances Thug’s over-the-top flows with London on da Track’s sparse, minor-key production. He performs at Regency Ballroom in San Francisco this Saturday.