Tank

The Tank is one of the cameo Monsters from the videogame Left 4 Dead that appears during the movie, along with the Boomer, Charger, Hunter, Smoker, and the Witch.

It was placed here because the directors originally planned to release Left 4 Dead exclusive DLC maps that featured the Cabin and the Facility. This idea was eventually scrapped when the company producing the DLC went bankrupt.

Physical Description and Attributes
The Tank has been heavily mutated by the Green Flu virus, and as a result, he has abnormal muscular growth is most obvious in his arms and upper body but less pronounced around the Tank's waist, hips, and legs. In addition, his body is covered with numerous scars and lesions, with an especially large open sore on his left pectoral. The Tank's jaw at first glance seems to be missing, but upon closer inspection it is shown to be enveloped within his thick neck muscles.

Its possible a vile of Boomer Bile could be used to summon the Tank from the Cabin's Cellar.

Appearances
The Tank does not appear during the sequence of the System Purge. However, he can be briefly spotted directly underneath Dana and Marty's cube cell as the camera pans-out.