Under rating threshold (hideshow)
Turn on all of the things that the achievement says are allowed, block off one entrance of the first map with fake walls, block off the second one with a few layers (I did 3) of walls and a hallway in the middle for you to shoot through, take out the pistol, hold down space, then click away from the browser so the game auto-shoots with the infinite pistol ammo. You'll be able to go do something else until level 21, but because the zombies clip through the walls if they stack up enough you wont be able to leave forever. It shortens your painfully dull playing time for the achievement by a good margin, and if the game's physics weren't so poor the achievement would essentially be automatic after the initial setup.
Under rating threshold (hideshow)
died because i was trying to act cool putting barrels around all the zombies than the devil shoots one of the barrels creating a chain reaction killing me
Under rating threshold (hideshow)
Completely unplayable for me. When i start a round it says "paused". then about 30 seconds later it unpauses, my character is flashing, and he runs up and left endlessly until he dies