Regression Simulator is a game seen in "The Vault" that lets Finn remember his past lives. 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.
- It is a clear reference to a real-life indie game called Super Hexagon.
- However, if you slow the video down, you will see that the level is impossible, if it was in Super Hexagon.