I played Betrayal at House on the Hill for the first time on the weekend. I was the traitor and it was haunt #38. I followed my interpretation of what the book said, which when the first person died read, and then said I did it wrong.
Note: The version is not the newest
The text (from memory):
Place as many firebats as there are players in the room where the Haunt started
Place 6 (total players) firebats in the room where the Haunt started
Place 1 (number of players in the room where the Haunt started) firebat in the room where the Haunt started.
Get out a number of firebats (represented by orange Bat tokens) equal to half the number of players, rounded up. Put them in the room where the haunt was revealed.
Was my interpretation correct?