Instructions
Start "Team Fortress 2" by inserting the game's disc. If you start the game anytime in the weeks around Halloween when the promotion is running, an update will automatically be detected.
Download any updates that are detected for your game. These will patch the game and add the items you will have to collect to unlock the Halloween achievements.
Complete the five "Scarechievements" while they are available. The achievements range from killing a spy in disguise to killing five players with a pumpkin bomb. To see the full list of achievements, press the "Xbox Media Button" in the center of your controller, press "View Achievements," and view "Team Fortress 2." The newly added achievements will be located at the very bottom of the list.