DO NOT PLACE CLEM'S HAT BEFORE ANY OF THESE AS IT WILL END THE EPISODE
1. Mrs. Disco Brocoli - This goes on AJ's bed.
2. Crystal - This goes on the desk next to AJ's bed.
3. James mask - This goes on coat rack next to the door.
4. Half Skull - This goes on the shelves with the rest of the skulls.
Do note that the achievement is buggy and you might get it after placing just one of the collectibles.