Simple idea but a very nice execution. I was surprised to see how much assets you've produced, good looking sprites all around. Actually working mirrors are a rarity, even on much bigger projects. Your intro slides are also very nice.
Having mirrors be the way to discover vampires is a stroke of genius, very nice touch. I love that you've given the player more than enough way to investigate monsters. One big problem however : since every guests arrive from the same door it's possible to simply camp in front of it. As soon as the "monster bar" get a spec of red, it's evident that the last arriving guest is a monster. One way to fix that would have been to have two or three differents doors.
Pretty solid entry overall, I would love to see this expended with more monsters. Nice job !