No-one Left Behind Achievement
No-one Left Behind20
Beat a campaign with all 4 Survivors.
Begin the No Mercy campaign on easy. Everyone must survive the last horde of Infected and make it into the rescue vehicle to get this achievement. It doesn’t matter if you have almost no health left, just as long as everyone walks into the rescue vehicle alive. This must be done in one sitting. You can't quit out and then continue from where you left off.