Edit: On a second watch there is also a grafiti symbol on the wall at the 0:04 mark. Looks like an upside down triangle and with a hand print with skull like markings. Maybe some sort of hybrid symbol of multiple deities?
When I first saw this I thought this was a mindwitness. Basically a beholder that underwent ceremorphosis. The eye stalks above the head and tentacles below but I'm not sure about the 2 eyes and nose of the skull. I wonder if it is just some random symbol.