We recently had need and occasion to use Flute of the Outer Gods twice in one game. (Which is bizarre by itself.) Then we disagreed about how it worked. It reads: 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.
There seem to be a few ways this could go down. Option one, the way I thought it worked:
1) Lose three stamina and three sanity and discard Flute of the Outer Gods.
2) Roll a combat check (no modifier, with all weapons, one success neccessary).
3) Win all monsters!
There's also a way to read it that requires getting to a combat check against one of the monsters. So it would work this way:
1) See a monster, let's say a zombie (or whatever, on a square with a gug, a dhole, a color out of space, and a flying polyp, or whatever you want to flute.)
2) Make a sanity check against one of the monsters (in this case, the zombie).
3) Now that it's time for a combat check, you can lose three stamina and three sanity and discard the flute.
4) Win all monsters!
It seems like there were more proposals too, these were just the most likely.
What do you guys do?