Runnats

A running carnivore that looks like a small greyhound, but it's descended from the common rat.
It is the size of a small dog of ancient times, and has a slender constitution and very long legs that are fit for running and chasing prey, and a tail that helps them retain balance. They extremly fast in short distances.
When it comes to small prey, they will run, chase and kill it, but their strategy is very different when it comes to larger creatures.
Their mouths are teeming with deadly bacteria, so a single bite from one of them will most likely result in a slow agonic death, with a stinking and rotting limb.
Usually, they will chase the prey and bite a leg slightly, then it will follow the injured animal for days, until the infection makes it weak enough, and then it will start eating it alive.
They usually hunt alone, and they will not kill people or animals that move in groups.
However they won't hesitate to make a move against an individual that strays from the group, or the guy that goes to a quiet place to take a leak or a shit.
Beware, these beasts may walk alone, but they are never alone. They live in hives of 2 + 1D6 individuals.
Once a bigger infected prey is weak enough, the stalker will call its buddies to partake in the feast, and to protect the prize from larger predators.
If one of them feels threatened, it will call for help, and the rest of the hive will come to its aid.
This is extremely undesirable, since the hives act in a stunningly coordinated fashion, in spite of not having a leader. A pack can easily tear a lonely human apart.
They do not reproduce as fast as their ancestors, but rather once a year, giving birth to 1-3 cubs.