So heres the thing, that video was a good idea, but I was actually talkin bout the characters from L4D, not the sequel. Also all I saw in that video was just reg zombies, none of the special ones. In my idea, I want to use every different kind of zombie, even the special ones. Now since L4D only have 4 survivors (hence the reason for the name of the game), in the mod they can have both survivors & special zombies. Now how to make the coding work to where the zombies wont attack the survivors, im sure its there somewhere. Anything is almost possible w/ the sdk. Also we can use either TF2 maps or levels from L4D or maybe either make a combo of both maps or even go a step further & create all new maps.
Now for a simple example (just throwin an idea in the air), an engi (happens to be my fav class) can setup a lvl 3 sg. Setup the coding correctly so that the sg will spot the zombie & think of it as an enemy & it will start firing on the zombie (just regular zombie mind u). Now of course when it comes to the Tank, it will have alot more health to it, so more or less it will be able to destroy the sg. Also depending upon the map, if the sg gets placed where alot of reg zombies can get to it, they will eventually destroy it.