you are supposed to go to the door in the room where the dancers were on the far right. in that room you got to suck up the ghosts that appear in the room and when your done, look at the mirror, it will show a switch on the opposite wall.
To all of those poor unlucky souls out there, this is for you:
If you don't watch Black Cat then Train Heartnet has a message for you:
I came to deliver some bad luck.