Before everything, beat the game first. (Unlock extra and custom night)

First, go to the extra section. Under animatronics, scroll until you get to RAT. Zoom as far as you can into his face. Try to center if you can. After waiting a bit, the screen should turn red and RAT should start shaking intensely. 7 numbers should appear on your screen. Note that the numbers are different for everyone. Enter those numbers into the custom night as shown on the previous screen. When you load in, check the stage with night vision on. There should be Shadow Candy. If not, try again. When you see Shadow Candy, go off of the camera. You will be jumpscared. Once you are jumpscared, you should be teleported to a new night. You cannot read the number of the night, since it is glitched out (that's part of the game). That's all you need to know about getting TO the shadow night. I may make an article about beating it if this article does good, since the shadow night is different than other nights.

Hopefully this helps!