Bestiary
Forty-plus variants, from the people who were simply standing here when it started to the cordon troops who died still wearing their plate. None of them are on a spawn timer you can learn.
Known variants
Forty-plus civilian variants — the people who were simply here when it happened. Slow, unarmoured and trivial one at a time. The problem is that they are never one at a time, and a rifle shot brings the rest of the street.
Fresher, faster and still capable of covering ground. They notice you sooner and commit harder. If something is closing rather than shambling, it is one of these.
Damaged badly enough that they no longer stand, and not slowed down nearly enough by it. They come along walkways and under vehicles, below your point of aim, and they are extremely easy to walk past.
The first responders, still in their vests and riot armour. Body shots stop meaning very much. Bring something that penetrates or start aiming higher.
The cordon did not hold, and the people manning it are still wearing full plate and helmets. The best-protected infected in the city, found exactly where the fighting was worst.
A special infected that does not respect cover, doorways or your plan for the building. Massive, durable and single-minded. This is what the Barrett is for, and you will still want the whole squad involved.
Behaviour
Infected are not delivered by an off-screen spawner at the edge of the level. They are already in the world, inside the things you walk past, and they come out when you get close enough to matter.
The practical effect is that clearing a street does not stay cleared, and that the route you scouted on the way in is not the route you will be walking on the way out — particularly if you were noisy about the objective.
Groups are seeded rather than scripted, so two runs at the same mission are not the same fight. Learn the map, by all means. It will not save you on its own.
Confirmed hiding places
Stay in the loop
Gameplay footage, build notes and the occasional honest post about what broke this week.