Flute of the Outer Gods
From Arkham Horror Wiki
Flute of the Outer Gods is a unique item. It first appeared in the Arkham Horror board game.
Card info
Any Phase: Lose 3 Sanity and 3 Stamina and discard Flute of the Outer Gods before making a Combat check to defeat all monsters in your current area. This does not affect Ancient Ones.
Price: $8
Clarification
You must pass a Horror Check before using the Flute. If there are more than one monster in your area, you only need to pass one Horror Check.