So last night I had a dream that I was in my house and there was random zombies for some reason. So somehow I ran to 2 fort and was being a spy and revolvering zombies. Somehow i ended up in the intel room with a lvl 2 sentry but one was sapping it. I started walking somewhere and i dont remember anymore. This was a real dream. After i woke up i thought about and came up with a l4d and tf2 hybrid. I typed this on my ipod touch and ill explain tomorrow when im off my ipod.

Edit: Alright it would be 9 on 9 versus and the survivors would be one of  every class. you would play on left 4 dead maps and just play it like it was left 4 dead except each class has their own special abilities. The scout can't get smokered. the soldier is the soldier. The pyro doesn't get hurt by fire. the engineer can build temp sentries. the heavy doesn't get knocked back when a tank hits him. The demoman can be the demoman. the medic can carry 3 first aid kits and can heal 100% instead of 80%. The sniper has piercing bullets. And he spah can turn invisible...