These are the guys in filth covered combat suits. They're not too tough, though taking on three or four at a time could get sticky, especially since they have been made somewhat tougher and it can take two or three shots to kill with the pistol. Also in the former human department, are the former human sergeants called shotgun guys. These guys are in black armor and are meaner and tougher than the zombies. Usually, they're not too much of a problem, but will turn you into swiss cheese if you're not careful.
Imps are brown, thorny hominids, which take several bullets to kill.
An imp can fry you with fire balls, or turn you into ground beef with their formidable claws. It's advisable to have something more potent than a pistol when taking on more than one of them. Demons are big, pink, and ugly. They're hard to kill, and have LOTS of teeth. Spectres are similar to demons, except they are nearly invisible.