my own zombies i think would be great in left 4 dead. the wraith [left], which stuns it's victims with extremely high-pitch screams. the reaper,[far right] crawls very slowly [since no legs] but can launch boney thorns out of it's arm, but if it's victim gets too close, it grabs and instantly KiIls them. then the scavenger [middle], which is extremely speedy on it's three legs, only attacks if shot, knocks down it's victims, steals all their ammo, and runs.