Instructions
Start the game on your PS3 console and select "Nacht der Untoten," "Verruckt," "Shi No Numa" or "Der Riese" as the map.
Play the game as you normally would until you find the mystery box. The mystery box spawns in a different location every game, so open doors to new areas of the map until you find it.
Walk up to the mystery box and press and hold the square button on your controller. Nine hundred fifty points will now be deducted from your points balance and a random weapon will pop up out of the box for you to grab. If it is labeled "M2 Flamethrower," press the square button pick it up.
Repeat the previous step until the "M2 Flamethrower" pops up out of the box. This may take several tries since the weapon order is random. If you run out of points, kill zombies until you have enough points to try again.