The point at which this plays is exactly what the title says on the tin. In-night, at rare points when you switch to a certain camera, you may see a hidden character somewhere in the camera. Leave your monitor on that cam for a few moments, then that character will acknowledge that you found them with a certain animation, then a moment later, the unlocking of that character will start pending. Beat the night after that happens, and congrats! You unlock that character to use in future nights! No need to worry if you get a Game Over, though. You'll get another shot at unlocking them once they appear on their corresponding cam again. I will first have Michelle, YES HER FROM PINY I K N O W , at the ready in the Plush Corner, where she will be napping with her back rested on Puppet's music box. She will open one eye (wink lol) to acknowledge that you found her. Tiffy, yes that... *rather peculiar* catgirl, and Fiinel, yes her the animal humanoid (idk she just cool) have also been thought up, but there will be many more to come, so stay tuned~
Mairusu, SEGA, and where it's due, among others.