What is this stuff?

I think conditions are too optional for this item to be somewhat useful. Maybe I misunderstand it ?

Creatures in Sky will attack you if you go out to the street anyway? Or am I wrong ?

Creatures in the Sky will move towards an investigator in a street area only when a Mythos card triggers their movement. With the Flare gun you force monsters in the Sky to reach you during the movement phase. This can be pretty helpful for various reasons; you can clear the Sky in a single round (you can have Flyers in the Sky with different dimensional symbols, so it's not certain that when a Mythos card instruct one of them to move, the others will follow), lowering the number of monsters on the board (remember that the Sky is considered to be part of Arkham, so the monsters in the Sky do count towards the monsters limit); or you can have some personal reasons to want monsters to attack you (a couple of Mi-go in the Sky are an invitation to fight); or, knowing some weaker characters will remain in the streets after the current round, you prefer being attacked rather than taking the risk monsters will attack your mates.

Or you can make a Nightgaunt descend from the Sky, only to fail the combat check and hitch-hiking into the nearest gate

Also, you can attack a monster in the street *and* use the flare gun (use it right as you move onto the space with the monster), clearing off even more stuff from the board. But... Eh ;') it's still not a very good card.

ok, thanks a lot. Now I got it.