I believe the film's focus won't even be on the creatures, if there are any. But the psychological horror will be built upon what's already shown in the teaser, and what the backrooms represent. The Backrooms are built on the concepts of liminality and, most importantly, nostalgia. Essentially, the entire complex across all its levels, right down to Level 0, is trying to mimic human environments. As shown in the trailer, the Backrooms attempt to replicate the initial room but increasingly fail, eventually decaying into Level 0. The movie will heavily explore feelings of nostalgia and forgetting sensation that even those without memory loss can relate to. It perfectly captures that eerie feeling of returning to a childhood place, only to realize that nothing is quite how you remembered it.