Sebastian
Sebastian is a character of the game who was once human, but was turned into what he is now by the same organization that you've been sent by to go through the facility. You can buy items from him in the pre-round shop and will have them ready for you when you start, and he also has a shop of his own around halfway through the playthrough that becomes available. He is passive with you unless you have a flash beacon, so its recommended to not flash him with it.
Imaginary Friend
The Imaginary Friend is a completely passive entity that only spawns if you have to come across the red controller that spawns it. Once the button has been pressed, it will appear a few seconds later and will occasionally talk to you as you play on. There is no way of getting rid of it unless you die and respawn, but besides it occasionally blocking your vision, it doesn't do much else.
Abstract Art
Abstract Art is another passive entity that you can come across during a playthrough. When you enter a room, you have a chance of one just standing in a random spot of the room and possibly even more than one. They are harmless though and they never move from their spot.Â
Painter
Painter is another entity in the game that you'll frequently come across during a playthrough. There are different ways to see Painter, but the most common one will be the screen next to fake doors and occasionally talking during the run. When opening a fake door that leads to one of the Good People, the screen next to the door that once displayed the room number will sometimes change into different text. It's not always the same, but it'll have different text such as ">:3", "please.stop.", "Sebastian asked me to do this", and ":(".