I did not quite understand how this was connected to the theme "Only One"
The monster looked great and scary. But when it chased me and I ran into a box it was just spinning around the box and nothing happened. Maybe make it so it wanders off after a while if you hide in a box.
There was no clear distinction on what you were supposed to do either. I figured out that I could pick up keys and that they could unlock doors but there was no clear visual distinction between keys and other objects so I ran around walking into objects trying to pick them up. I would recomend adding some sort of visual indicator to interactable objects. The game could also use some more ambient sounds such as steps from walking and random creaks and ominous distant sounds.
Could not figure out how to run, would be interesting to have the ability to run for short bursts to increase the intensity of chase sequences.