Locate which basement that the sounds are coming from, if you aren't hearing anything inside of them than you are probably the thing you want to get rid of.

In order to get rid of him you must know where he is. Open the door and look, very simple!

No demons can attack you if they are stunned, proceed to continuously throwing the grenade until their screams can pierce your ears. When that happens you can proceed to the next step without risking any chances of death!

Dash down there and turn on the lights, it is known that those figures disappear instantly after you turn them on. Though you should be careful as leaving the room will cause the lights to be turned back off!

Open your spawn menu by pressing (TAB) and summon a thin circular building prop that is a size of a NPC, after that proceed to place a couple of beers around it The More The Better so fit as much as you can.

Summon a Kleiner NPC and proceed to kill it with a crowbar, make it sure he lands inside the circle!

Once Kleiner is at the ground dead, turn off the lights but be quick as the shadows will show up, activate the sacrifice by interacting with the corpse.

Once activated, beers will start to combust into flames one at a time as the room gets more blue by the second.
A Bunch of Barneys will slowly rise from the ground below and start saying voicelines.
Once that is complete, the room will get blasted with screams as the Barneys slowly leaves while grabbing both the corpse and the shadow figures down with them.

Congratulations, the shadow figure is gone and now you have successfully wasted 3 minutes reading this unhelpful guide!