I can't seem to defeat the black monster thing, because he kills me even when he's dead... am I missing a different way to kill him then leaving the room? Other then that from what I've seen the idea is really nice and original, but I think you should put the information you have on the game page also on here if you can (I don't know if you can :/)
Viewing post in Nil and the Chamber of Echoes jam comments
What you want to do is pass by his corpse without touching it and go back up to the main room through the right hallway, there will be a key in the hallway. You need 2 keys to beat the game, so good luck getting the other! Also I unfortunately don't have the ability to add the info, sorry for the inconvenience :(