This is an easy method to get the Untouchables Achievement in Left 4 Dead, Played on the No Mercy Campaign on Easy difficulty without using the "Jesus Room".

Untouchables Achievement: No Survivors take damage after contacting the rescue vehicle.


It is important to have 3 other players (non bots) play with you while attempting this. Otherwise bots will do whatever they feel like doing and you have no control on the strategy. The trick is to stay on the very top of the roof and have 2 players on both air conditions units. Have two players use shotguns and two players use rifles. Have 2 players facing forward and 2 players facing backwards. 4 Average L4D players can complete this achievement easily. Watch the video below for more details.