Level -1.5 has yet to be confirmed. However, there is one singular fragment of data recorded about the level.
User u/spartanwolf223 had apparently been thrown into Level -1.5 after he was forced onto the floor on Level 1.5.
Description
All we got was this user's post. We can get some information from it, but it's still very little. Expeditions to this level are still under consideration.
The Post
Oh lord, forgive me please. I have ignored the warnings of the fake windows.. and I ended in room -1.5. God I'm so stupid! The colors.. oh my god... the colors. My brain.. my brain cannot comprehend them. But it's okay now. The colors are gone. And so is everything else. Okay, I need to explain this. DO NOT LAY DOWN IN ROOM 1.5 The colors... they hurt so bad, but you must keep moving. Do not touch the floor with anything other than your feet. If you do.. then you join me. I laid down, and I was... suddenly pulled out of the room. I was pulled along a corridor at astonishing speeds, and I thought I had escaped. Ha! Escaped... But it was much worse. I was slammed into a wall... well I thought that's what would happen. I went straight through into nothing. I don't know how long I was there, but my watch was counting back. I had the stopwatch on so I knew how long I had been in the backrooms, and it counted back. But it went past zero. It stopped at -1.5, just as I landed in a new room. This room... it's just water. The walls, the floor, the ceiling, the doors, are all water. But it doesn't flow. You can't touch it. God it's so cold here... I need to keep moving. Certain parts of this room... there is nothing. It's just a void. You can tell when you enter these parts, as you feel nothing. Your entire body is gone. I couldn't see myself. Please don't follow me. I don't know what's in this room... and I don't want to find out. Please... for your own safety.. oh who am I kidding. These rooms are never safe. I'm not safe, that's for sure. And I know that because of the creature that is standing in front of me, waiting. Waiting for me to finish this post? Ha.. I guess I'll see. Hope you guys aren't suffering like I am.