Shoot the ten lanterns in the Prologue / Groesten Haus (Zombies) map to unlock the Mystery Box. This is very useful for getting the "Pressure Cooker" achievement (complete Round 20 in the Prologue). Eight lanterns are inside the house (four downstairs and four upstairs) and two are outside (left window and right window). After shooting a lantern, it will make a raven sound and start glowing purple. After shooting all ten lanterns, a door will open upstairs and reveal the secret Mystery Box behind it. It costs 1,000 points to use and gives you one random weapon. It can also give you the Jack-In-The-Box, which distracts zombies for a few seconds and kills them upon detonation.