This two-video series explores how the scoring to the video game Portal 2, published by Valve Corporation, not only helps tell the game’s story, but also comments on the game developers’ philosophy of puzzle design. The first video explores how the game’s title theme 9999999, including its texture, voice leadings, and chord qualities, musically enacts dual aspects of the character of the game’s central antagonist GlaDOS: once human, her personality was uploaded into a computer mainframe where she has become a sociopathic, homicidal artificial intelligence who takes delight in subjecting humans to hazardous scientific experimentation. The second video demonstrates that 9999999 serves as the theme for a set of double variations in the game’s middle act. Since Valve’s philosophy of player training centers on iterative puzzle-design that systematically increase in complexity, and the musical accompaniments for these puzzles feature coordinated developments in musical complexity, the scoring here lets us parse the puzzle design into a kind of set of gameplay theme-and-variations.