I was googling portfolios and websites from people who worked on Nickelodeon back in the 90s and I had found Karim Miteff's online resume. He's the co-creator of Nick Arcade.
What really caught my eyes was a pilot of a game show called "Haunted House Party". You can fully download it on his website.
The shows "ghost" (Karim Miteff himself, I think) looks like Beetlejuice. The kids went to a Haunted House Party and started disappearing in the house. They have to answer some questions correctly and, in this pilot, catch ghosts as in Ghostbusters in order to avoid it. As they complete these objectives, they gain time to save the other kids at the end. The clock strikes at certain time and one of the kids disappear. Only one player is left, and the last objective is the rescue mission (but you would only know what happened if the pilot became a series).
I don't think that counts as Lost + Found media, but sure counts as an unreleased series. I'm not sure if it became a series after all. Please correct me if I'm wrong.
Since the link seems to now lead to a directory, I took a look at the archived page mentioned in this post and by some miracle was able to download the referenced video.