Regression Simulator is a game seen in "The Vault" that lets Finn remember his past lives. It is a clear reference to a real-life indie game called Super Hexagon. Jake downloads it onto BMO and shows it to Finn, claiming Lady Rainicorn said it is good. On starting the game, a rotating red hexagon appears on the screen, and a deep voice says, "Welcome, adventurer. I am the Hypno-Priest. I will be your guide. Deep into your subconscious mind. Follow me now, adventurer." When Finn enters the vault, he sees his past lives: a comet, a butterfly, a "thing," and Shoko. The game ends after Finn remembers falling into the radioactive river as Shoko.