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Collecting the letters found in certain levels as Biker will unlock additional dialogue when talking to the characters in the basement at the end of chapter 19. While normally they will refer to their scheme as just a game, when all of the letters have been collected, they will reveal a much deeper conspiracy present within the game.
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While the translation is mostly aesthetic, the mask does add some unique dialogue for the ending of the Bonus Chapter Highball:
"Salut, je suis Wiley Wiggins! Bienvenue a fantastic arcade!"
which translates to "Hello, I am Wily Wiggins! Welcome to Fantastic Arcade!"
This is in reference to the festival "Fantastic Arcade", which named Hotline Miami as "Most Fantastic" in 2012.
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