A zombie map made by LoveLess and myself (lil-Inferno). I did the ambulance triggers whereas LoveLess did... everything else.

Zombies will spawn on the side of the map and will attack buildings, eventually raiding them and running helpless Civilians out of them. When a certain amount of Civilians are killed, it's game over. Zombies also have variable health (their shields will sporadically changed). When you die, an ambulance will rush towards your location, pick up your body, and bring it back to the hospital. It will also do this for every NPC Marine, although it takes players as a priority.