How about… a titanic zombie? Super slow, super huge. Trying to ram it is like trying to ram several metal walls. Requires a lot of firepower to take down, and can take hours to butcher. Very slow, but can squish a survivor like an ant.
Or boomer like creatures that explode into thick goo. Can slow and weigh down a survivor or his/her car. Require car repairs to scrape off the goo.
For more zombie evolutions, from the slavering biter, to the saber-toothed biter? Faster than before, but not as fast and doesn’t have the night vision of predators. Special bite attack that causes bleeding on a random part and also functions as a grab that causes large amounts of pain.
Looking at the thing/tentacle dog that’s sometimes in the mines… how about a zombie, that at first, looks like a normal zombie when you see it walking around the map. Get too close, however… and something bursts out of it, something much nastier.
It could be some sort of blob-shoggoth-zombie hollow like creature. Lower body still human, upper body a mass of writhing (and sharp) tentacle-like growths. Or we could go full xenomorph and have a real nasty creature burst out, one with a very fast evolution where it becomes a race to kill it before it turns into something real deadly.
Or some sort of genetically unstable zombie. Every once in a while this zombie would mutate, gaining (or losing) several mutations. Like… it grows claws (increased cutting damage), it becomes more aware (increased vision radius), it hardens (slows down, increases defense).
In fact, how about zombie traps for vehicles. At first glance it looks like a corpse in the road, you ignore it and try to run over it and continue driving. However, like a mine or a blade trap it detects you once you enter it’s radius, and it self-destructs, spraying a fountain of acid everywhere. Car gets badly damaged.