During my play through with some friends earlier i seem to have discovered a second smoke monster (a hallucination) within the prisons.
I was at the corridor that has the hammer and a monster appeared and somehow I was paralyzed and the monster came up and killed me which i thought was rather odd, it was much like a cut scene.
Anyway I die and when i reload i am within on of the cells with a monster within the doorway which then just dissolves in front of me.
Anyway it was weird and I thought I would share. I know that there is another monster hallucination earlier in the game... Yeah I drank a lot of coffee, so what