The lifeform is the misremembered evolution of still life

I don't know if Kane would plan this to be the case. But I do think it is possible to be the case. The backrooms misremembers a normal room into just barren yellow hallways. The still life all have different functions since people are different.

The still life themselves a lot aren't even hostile. And the ones that are, are weaker and easier to get away from then the lifeform. The most troublesome still life being FF3 and Pirate Clark. If the still life is analogous to the first or second copy of a room. The lifeform is near the end, the barren yellow hallway version of a human. Combined with bacteria. Stick figures. And it's possible that if pirate Clark somehow escapes. It could become a lifeform. But this isn't required for this theory.

The lifeform despite looking a lot less human. Are much stronger, faster, and good at hunting than the still life. As if it was evolving to kill. The lifeform is able to mimic to lure people and knows when a person is suspicious of it. Compared to the still life who either don't have a goal, or performs low level communication. The still life best at hunting seems to be Pirate Clark. and FF3. With results below the lifeform.

Story wise this also works. Humans become misremembered to just a lifeform that kills. The basest view one could have of a human. A view many hunted animals would have of humans. Simply monsters. The lifeform is that but in a truly literal sense.