The tonsil stone is required to access this area. A lot of blood stone enemies(the equivalent of titanite lizards from Dark Souls), along with a different version that attacks back. All I know is that this is missing 99% of the level, this game has been out for a while and I dunno what to make of it. Also to new players, be careful with a certain enemy towards the boss door that resembles a brain head with eyes coming out of it. If you get in it's view, you'll start to get frenzy, QUICKLY.