This might be a hot take, but I thought what they did for the "monster" of the Backrooms was ABSOLUTELY GENIUS! How it organically builds upon how the Backrooms work, how it connects to the real world and its people (specifically Clark), and how it creates something that is dangerous and terrifying, and yet at the same time, frighteningly human!

Let me ask you something. Do you think it's interesting that out of all the "people" that were in the Backrooms, Clark's was the only one that was actually dangerous and was actually going around killing people? That's because the Backrooms remembers things in the real world, and "the more times it remembers, the less it does" until it only remembers the details that stand out the most, like how, when you remember a childhood bedroom, you only remember specific furniture or decorations. And the same goes for people!

Because Clark's life is dominated by his anxieties, frustration, fears, and, most importantly, his desire to lash out at everything he thinks is to blame, the Backrooms only remembered those negative feelings. And eventually they all culminated into this dangerous entity. Just like how he lashed out and attacked others that he believes are the fault of where he is, this entity of his own (unintentional) making lashes out and attacks everyone in sight, because, as you can see by the expression on its face, it too is driven by those same anxieties and fears!

Eye test.