What Are "Things"?
"Things" is used as a broad term to refer to any crude, unearthly living beings that can be found in the Backrooms that are definitely neither human or earth-native animal. While rare in most levels, they are in almost all cases extremely dangerous, and should never be approached unless you know what the hell you're going to do.
"Things" can range in size, width, girth, behavior, etc., pretty any way living things on Living Earth vary from each other. While most seemingly defend their "home" (The Backrooms) from us, some of them are smart enough to be directly malicious to us for their own gain.
With the exception of regular Class 5 levels, sighting of "Things" in even Class 4 levels are rare, and it is believed that some "Things" may not exist at all.