This is actually one of your better actual games! I assume Slenderman was a major influence for making this one? This game sure shares a lot of similarities with Slenderman to say the least. My favorite part was that there's no "suddenly in your face scary thing" at the end, I hate those.
I wouldn't quite say there was a lot of entirely brand new lore here. We've already seen a lot of the Moon King and seeing the South Star Church mentioned here confirms my suspicion that The Shovel is part of the origin story for Clear Moon and/or its leader. And it looks like the burned chapel in this game is the same one from Oh Chapel.
So there's a lot of connections between your seemingly random works and the antagonist organization of your more popular works (Dead Detention for example), but how about those mysterious footprints? Does the Moon King/Dr. Mason/Mr. Noom (3rd one I assume is mostly fake) have a bestial form more powerful than his tall, black figure form that Max and Shia fought in the Dead Detention 2 finale or did those monster footprints come from something else entirely? Can only wonder at this point.
For those trying to find 15+ items, a few hints I can give are that there's 4 items at the starting area, nothing north of Atom's photo, 1 or 2 things a little ways south of the robe and 3 tombstones right next to each other that count as 3 things. Also, when viewing the messages on the smart phone, you can click them to get a closer look at them (I didn't figure that out right away).