Fright Night was developed by @GamesProductionOfficial in 2016. I found these teasers on the developer's deviantart profile. I learned about this game from a video by @O5carMagu1re . Under that video, I saw a comment by user siroscar8922. The translation of that comment (or rather, the excerpt that specifically talks about the game):

"A friend of mine made a video many years ago about canceled FNAF fangames showing Fright Night, and let me mention that after that user's video was uploaded, Games Production showed up, commenting that the game would be back. Nothing happened, but that was many years ago in the pre-SL era. Besides, they also showed the trailer, which looked like a Scooby-Doo theme. Haha.

As for the unconfirmed existence, they did exist as such but with builds…»

If you have any information about the game, or any other content about it, please write in the comments.