I'm digging the ninja/martial artist idea. ... A lamb/sheep related beast works fine.
It has been said that it is fear of the unknown which is the cause of the most base terror, and this veiled assassin makes the most of that fact.
AT first there were mere whispers from the far east: families found dead in their beds, killed in the night, their near neighbours none the wiser. Only two things linked the deaths; the complete lack of noise during the night, the cause of death - blunt trauma to the neck.
It took some time, but eventually a detective with an eye for the big picture saw another pattern: there were no vegetarians among any of the dead.
Soon meat eaters everywhere were passing rumours among themselves. Eschewing meat was the only way be safe. reciting the phrase mint sauce
into a mirror three times would summon the small, deceptively cute shadow into your home and that would be the last thing you saw.
And then, one more rumour. No one knew where it came from, nor how accurate it was, but some say, quietly, on some nights of the killings a lone person heard the blood-freezing war cry of the killer......baaa