For those with Left 4 Dead 2’s new DLC, The Passing, the first “mutation” mode is out to play now.
The mode is named “Bleed Out” and puts players in the normal campaign with constantly deteriorating health. The only way to stop yourself from dying in the mode will be to use then temporary health-boosting items pills and adrenaline. Apparently we’ll be seeing “over 20” mutations [link], which will be out weekly.
Take a look over at the Left 4 Dead 2 homepage if you’d like to see screenshots, videos and suchlike.