This guide explains you how to get the ? keycard.
How to Shoot The Crow
Select the scout as your character. Go to the roof, and look around until you see a crow flying around.
Then get your slingshot. The shot is tricky and may take a few attempts, but with practice its easy.
Finding the Keycard
Finding the keycard can be hard so make sure you see where the crow is hit. When dropped, the keycard looks like this.
Opening the Door
When you get the keycard, find this door.
It is spoiler:
Upstairs from the closet room.
Do not read this unless you want to be spoiled.
This is what's inside: