I've been seeing dicussion circle around about a certain topic, so I'm here to clarify: Beating all of the custom night challenges DOES NOT grant a new "harder max mode." All you get is the yellow star on the title screen.
The impossible night easter egg was removed because people used extreme exploits and glitches to beat it which ruined the fun of it. It was accessed by pressing the "i" key in the custom night menu a few times. It was not an unlockable and it was not meant to be possible. It is not present in the current version of the game either.
(Reposted because when I posted it on mobile it didn't post as a devlog.)