Secret Code in the End Credits
I just completed the game and I noticed something interesting in the end credits.
Letting them scroll to the bottom without skipping, you can hear Mike say: “What is that?” and after that this secret code is displayed:
New Game+ Mode
Once you beat the game on horror, you are eligable to use it in the main menu. This code unlocks a New Game+ mode where you have literally everything right at the start.